MONTHLY GLOBAL TROPICAL CYCLONE SUMMARY
SEPTEMBER, 2007
Part 1 of 3
(For general comments about the nature of these summaries, as well as
information on how to download the tabular cyclone track files, see
the Author's Note at the end of this summary.)
NOTE!!! The September summary is being issued in three installments. The
first covers the Atlantic basin. The second will cover the Northeast
Pacific and North Indian Ocean basins, plus contain an extra feature.
The third will cover the Northwest Pacific basin.
*************************************************************************
SEPTEMBER HIGHLIGHTS
--> Destructive Category 5 hurricane strikes Nicaragua
--> Typhoons strike Korea and China
--> Eight Atlantic tropical storms in September ties record for month
*************************************************************************
WIKIPEDIA TROPICAL CYCLONE REPORTS
Short reports with satellite pictures and small-scale maps for all
tropical cyclones may be found at the following links:
http://en.wikipedia.org/wiki/2007_Atlantic_hurricane_season
http://en.wikipedia.org/wiki/2007_Pacific_hurricane_season
http://en.wikipedia.org/wiki/2007_Pacific_typhoon_season
http://en.wikipedia.org/wiki/2007_North_Indian_cyclone_season
http://en.wikipedia.org/wiki/2007-08_Southern_Hemisphere_tropical_cyclone_se
ason
For some storms more detailed reports have been prepared. In those cases
I will include the specific links in the reports for the applicable
tropical cyclones.
*************************************************************************
ACTIVITY BY BASINS
ATLANTIC (ATL) - North Atlantic Ocean, Caribbean Sea, Gulf of Mexico
Activity for September: 1 tropical depression
4 tropical storms
3 hurricanes **
1 intense hurricane
** - one of these was treated operationally as a strong tropical storm
but was upgraded to hurricane status during post-storm analysis
Sources of Information
----------------------
Most of the information presented below was obtained from the
various tropical cyclone products issued by the Tropical Prediction
Center/National Hurricane Center (TPC/NHC) in Miami, Florida:
discussions, public advisories, forecast/advisories, tropical weather
outlooks, special tropical disturbance statements, etc. Some
additional information may have been gleaned from the monthly
summaries prepared by the hurricane specialists and available on
TPC/NHC's website. All references to sustained winds imply a
1-minute averaging period unless otherwise noted.
Atlantic Tropical Activity for September
----------------------------------------
The month of September was paradoxical: it was very active, very
quiet, and average all at the same time--depending on which parameters
one considers. Over the period 1950-2000, the average number of named
storms in September is 3.4--in 2007 there were 8, tying the record set
in September, 2002. The average numbers of hurricanes and intense
hurricanes over the same period are 2.4 and 1.3, respectively. In
September, 2007, there were 4 hurricanes and 1 intense hurricane. So as
far as numbers of storms and hurricanes go, the month was quite active.
However, in terms of the longevity of the storms, the month was well
below normal. For the 1950-2000 period, the average numbers of NSD, HD,
and IHD are 21.7, 12.3, and 3.0, respectively. September of 2007
featured 16.3 NSD, 3.5 HD, and 2.0 IHD. Most of the storms were quite
short-lived with Humberto, Jerry, Lorenzo and Melissa existing as a NS
for less than two days, and Gabrielle and Ingrid were at tropical or
subtropical storm intensity for not much more than two days.
So in the numbers of storms department (NS, H, IH), September was
160% of the 1950-2000 average. But in terms of the longevity parameters
(NSD, HD, IHD), the month was only 57% of normal. According to figures
from Phil Klotzbach and the CSU seasonal forecasting team, the NTC for
September, 2007, was 47%--very near the long-term average of 48% for the
month.
The main event of the month was Hurricane Felix, which made landfall
in northeastern Nicaragua as a potentially catastrophic Category 5
hurricane. Hurricane Humberto gained considerable attention when it
intensified from a tropical disturbance to a strong Category 1 hurricane
in less than 24 hours just offshore from the Texas coast. Humberto
became the first landfalling U. S. hurricane since Hurricane Wilma in
October, 2005. Tropical Storm Gabrielle was the only other tropical
cyclone during the month to make a U. S. landfall when it passed over
the Outer Banks of North Carolina. Late in the month, Lorenzo
strengthened just about as quickly as Humberto had done and made landfall
along the Mexican coast very near the same point where Hurricane Dean
had struck about a month earlier.
Strong upper-level LOWs were more frequent than usual across the
tropical Atlantic during September, and were responsible for the early
demise of storms Ingrid, Karen and Melissa by inducing strong westerly
shear over the cyclones. The formation of these three storms over the
eastern and central tropical Atlantic was consistent with what often
happens in very active seasons, and had the upper-level LOWs been absent
and a strong subtropical ridge been present, things could have been very
different for the Antilles and possibly the southeastern U. S.
Official TPC/NHC reports for all the 2007 tropical cyclones except
for Hurricanes Dean, Felix and Noel and Tropical Storm Erin are now
available online at the following URL:
http://www.nhc.noaa.gov/2007atlan.shtml
I have written a more full report on Hurricane Felix. For the other
storms I have written shorter reports but have included some discussion
on various topics which I hope will be interesting. Links to all the
Wikipedia reports are included in the write-up for each individual
cyclone.
!!!!!!!!!! ADDENDUM TO AUGUST SUMMARY !!!!!!!!!!
In the August summary I included a write-up about an interesting low-
pressure area southeast of the New England coast at the end of August
and into the early days of September. (See the August summary for more
details.) The question was raised as to whether this system might
qualify for inclusion as an unnamed tropical storm. I asked Eric Blake
if this system (identified at the time as Invest 96L) was being
considered as a potential after-the-fact tropical storm.
The answer is that it is not. Following is Eric's reply:
"Perhaps it was a weak TD, but it is not being seriously considered as a
TS. There is no evidence of TS-force winds (that QuikScat pass doesn't
show reliable TS winds--those wind vectors are not the correct solution
for a cyclonic storm!) in any data source. The system from last year
(i.e., the unnamed July, 2006, storm) was much more wound up."
HURRICANE FELIX
(TC-06)
31 August - 5 September
-------------------------------------------
A. Synoptic History
-------------------
Felix formed from a tropical wave that moved westward off the coast
of Africa on 24 August. Little convective activity was noted for several
days, but by the 28th the system began to show signs of organization.
This trend toward improving convective organization continued over the
next few days, and on the afternoon of 31 August an Air Force Reserves
reconnaissance plane found a closed surface circulation with FLWs of
36 kts, equating to about 30 kts at the surface. Hence, advisories
were initiated on Tropical Depression 06 at 2100 UTC. The center of
TD-06 was initially located about 155 nm east-southeast of the Windward
Islands, moving toward the west at 14 kts. The convection continued
to consolidate during the night as the system moved through the southern
Windwards, and Tropical Storm Felix was christened at 0900 UTC on
1 September with the center located about 25 nm northwest of the island
of Grenada.
The storm was moving westward at a pretty good clip (16 kts) as it was
steered by a ridge to the north. Felix intensified rapidly and was
upgraded to a hurricane at 02/0000 UTC while located about 235 nm east
of Aruba. A reconnaissance plane had found 77-kt winds at a flight level
of 2286 m, and the SFMR found surface winds of 65 kts. A CP of 993 mb
was measured within a 30-nm wide eye. Felix passed just north of the
ABC islands as it continued to intensify. Within 24 hours after
initially reaching hurricane intensity, the storm had become a very
intense Category 5 hurricane on the Saffir/Simpson scale while located
approximately 340 nm southeast of Kingston, Jamaica.
TPC/NHC issued a special advisory at 03/0000 UTC. From the Discussion
Bulletin:
"Reports from a NOAA Hurricane Hunter aircraft indicate that Felix has
intensified and is now a Category 5 hurricane. The aircraft reported
peak flight-level winds of 152 kts, with peak SFMR winds of 142 kts in
the southwest quadrant. Higher SFMR winds were found in the northeast
quadrant, up to 163 kts, but these may have been contaminated by graupel.
A dropsonde released in the southwest quadrant landed in the northeast
quadrant, and this drop yielded a surface estimate of 139 kts based on
the lowest 150 m layer average. Based on these data, the peak surface
winds are estimated to be at least 145 kts. An eye sonde measured a
surface pressure of 936 mb with surface winds of 24 kts. Because of
the extreme turbulence and graupel that the aircraft experienced, the
mission is being aborted and the aircraft is returning to St. Croix."
Given that the drop which measured the 936 mb CP reported winds as
high as 24 kts, it was assumed that it missed the center of the eye.
The CP reported in the 0000 UTC special advisory was adjusted to 934 mb.
The MSW inferred from all the data is surprisingly high for a CP no lower
than 934 mb, and it seems likely there is a good chance the MSW could be
upped even higher during post-storm analysis and review. At its peak
Felix was a small cyclone, with hurricane-force winds extending outward
about 20 nm from the center and gales covering an area less than 200 nm
in diameter.
The pressure dropped as low as 929 mb at around 03/0900 UTC, but began
to rise thereafter as Felix underwent an eyewall replacement cycle. The
145-kt intensity was maintained for 18 hours, but the MSW began to drop
after 1200 UTC, falling to 115 kts by 04/0000 UTC. However, Felix
completed the eyewall cycle and began to steadily re-intensify as it
approached the Nicaraguan coast. At 04/0900 UTC the center of Felix was
only about 55 nm southeast of Cabo Gracias a Dios on the Nicaragua/
Honduras border. After having risen to 953 mb at 0000 UTC, the CP had
fallen to 939 mb and a reconnaissance plane had found a peak FLW of
148 kts, corresponding to 133 kts at the surface, and dropsonde data
analysis supported a surface wind of 132 kts. Based on these data, the
MSW was upped to 135 kts, and at 1200 UTC, shortly before landfall,
Felix was re-upgraded to Category 5 status with 140-kt winds. Aircraft
data supported 135 kts at 0700 UTC, and after that time the eye became
more distinct and the surrounding cloud tops cooled, resulting in an
increase in Objective T-numbers of 0.3.
Potentially-catastrophic Hurricane Felix made landfall around 1200 UTC
in extreme northeastern Nicaragua very near Punta Gorda, or about 15 km
north-northeast of Puerto Cabezas. Following landfall Felix began to
quickly weaken as it continued westward over the mountainous terrain
of northern Nicaragua. The storm had weakened to tropical storm status
by 05/0000 UTC, and the final NHC advisory was issued at 0900 UTC,
downgrading the system to a depression near Tegucigalpa, Honduras.
The official TPC/NHC report on Felix is not yet available online, but
the very detailed Wikipedia report on Hurricane Felix may be found at
the following link:
http://en.wikipedia.org/wiki/Hurricane_Felix_%282007%29
B. Storm Impacts
----------------
Only minor damage from Felix was sustained in the southern Windward
Islands. The major impact from the hurricane was in Central America,
primarily in Nicaragua.
According to the Wikipedia report, damage was severe in Nicaragua and
Honduras. In Puerto Cabezas, Nicaragua, nearly every structure sustained
roof damage, and many buildings were destroyed. On the Miskito Cays,
which lie about 70 km off the coast of northeastern Nicaragua, every
house was completely destroyed. At least 133 persons are known to have
died, 130 of them in Nicaragua. Also, hundreds of others have been
reported missing. Over 9000 houses were destroyed, most in Puerto
Cabezas (also known as Bilwi). Inland flooding was also reported in
Honduras, particularly near Tegucigalpa and in the northwestern portion
of the nation.
C. Comparison with Hurricane Edith of 1971
------------------------------------------
It would be remiss not to call attention to the similarities between
Hurricane Felix and another intense Caribbean hurricane over a third of
a century earlier--Hurricane Edith of 1971. The two hurricanes
exhibited remarkable similarities in size, track, dates of occurrence,
and intensity. In fact, they could almost be called identical twins.
(1) Size - Like Felix, Edith was a very small tropical cyclone at its
peak. Reconnaissance crews likened the storm to a giant tornado
with a perfectly-formed eye only five miles in diameter.
(2) Track - Like Felix, Edith became a tropical depression just east
of the southern Windward Islands, passed very near Grenada and
later just north of the ABC islands, and eventually slammed into
northeastern Nicaragua slightly north of Felix' landfall point.
However, the similarity ends there. Instead of dissipating over
mountainous Central America, Edith veered to the west-northwest,
emerging into the Gulf of Honduras before making a second landfall
in extreme northern Belize. The storm then crossed the Bay of
Campeche, and for awhile it looked as if Edith would move into
northern Mexico as a minimal tropical storm and quietly dissipate.
However, when almost straddling the Mexican coastline, Edith veered
sharply to the north and later north-northeast, re-intensified, and
made landfall in western Louisiana as a Category 2 hurricane.
(3) Dates - Felix formed as a tropical depression on 31 August and made
landfall in Nicaragua on 4 September. Edith occurred only a few
days later by the calendar, forming on 6 September and making its
Nicaraguan landfall late on the 9th. Another slight difference
between the two storms is that Edith was not upgraded to tropical
storm status quite as far east as Felix. The earlier storm reached
tropical storm intensity while passing just north of the ABC islands
whereas Felix was reaching hurricane intensity in the same location.
(4) Intensity - The Atlantic Best Track file gives for Edith a peak MSW
of 140 kts with a minimum CP of 943 mb. Admittedly, 140 kts has
always seemed a bit too high for 943 mb. However, Felix' dimensions
of 934 mb and 145 kts makes Edith's peak parameters much more
believable. Operationally, Edith's peak MSW was reported at
150 kts at one point, but this was apparently reduced during post-
storm analysis, very possibly because of the rather high minimum
central pressure.
The meteorological service in British Honduras (now Belize) reported
that there were 100 fatalities and 7000 persons left homeless in the
Cape Gracias area as a result of Hurricane Edith, so the impact of the
two hurricanes in that region seems to also be similar. (Note: The
above information on Hurricane Edith is taken collectively from the
author's memory and from the preliminary report on the storm written
by John R. Hope, who was then a forecaster at NHC.)
(Report written by Gary Padgett)
SUBTROPICAL/TROPICAL STORM GABRIELLE
(TC-07)
4 - 12 September
--------------------------------------------------------
A. Synoptic History
-------------------
A non-tropical LOW formed off the southeastern U. S. coast on
3 September and for the next several days moved slowly eastward in the
general direction of Bermuda. The LOW became better defined late on the
7th and was upgraded to Subtropical Storm Gabrielle at 08/0000 UTC while
located about 360 nm southeast of Cape Hatteras. Gabrielle moved north-
westward and slowly acquired tropical characteristics and was classified
as a tropical storm at 2100 UTC that day. The cyclone strengthened
early on the 9th and reached a peak intensity of 50 kts while located
just south-southeast of Cape Lookout, North Carolina. A few hours later,
the center made landfall along the Cape Lookout National Seashore.
After making landfall, Gabrielle turned northeastward and weakened
due to land interaction and northerly wind shear. The storm moved back
out over the Atlantic early on 10 September near Kill Devil Hills, North
Carolina, and weakened to a tropical depression a few hours later. On
the 11th the circulation became ill-defined and the depression dissipated
about 260 nm south of Nova Scotia. Heavy rainfall associated with
Gabrielle was confined to a rather small area near Cape Lookout.
Overall, the impacts from Tropical Storm Gabrielle in eastern North
Carolina were minimal.
B. Discussion
-------------
Operationally, the highest winds reported for Gabrielle were 45 kts.
During post-storm analysis, it was determined that the storm reached a
peak MSW of 50 kts. This was based on a peak 925-mb FLW of 61 kts and
a later 850-mb FLW of 66 kts on the morning of 9 September. A dropsonde
around the same time reported a surface wind of 49 kts. Even though
Gabrielle's intensity is estimated at 50 kts around the time of landfall,
these strong winds never reached the coast due to northerly shear which
kept the strongest thunderstorm activity offshore for several hours.
The highest sustained wind measured in eastern North Carolina was 38 kts
at Frisco Pier. A gust to 46 kts was reported at Cape Hatteras, and a
gust to 53 kts was observed at Ocracoke. Four to eight inches of rain
fell across southern Craven and eastern Carteret Counties with a
maximum of 9.03 inches (229.4 mm) near Harlowe in Carteret County.
Rich Henning, a member of the 53rd Weather Reconnaissance Squadron,
was on the flight into Gabrielle which measured the 61-kt FLW early on
the 9th. In Rich's opinion, what caused the sudden intensification of
the storm was a mesoscale convective event which just happened to be
superimposed near the core of a tropical cyclone, but which did not
result in a sustained intensification of the "parent vortex". The
plane found an environment with lots of shear, dry air, and trough
interaction--bad things for a barotropic vortex but a trigger for
thunderstorm activity. Rich notes that a similar convective burst led
to the intensification of Tropical Storm Marco of 1996 to hurricane
intensity. As soon as the convective feature dissipated, Marco weakened
back to a fairly weak, sheared tropical storm.
During the several days when the parent LOW which spawned Gabrielle
was meandering around between the U. S. and Bermuda, there were some
reports circulating in the media that the LOW might spawn a Category 2
hurricane which would race up the coast toward New York. Whether or not
any of the numerical models were suggesting this, I do not know.
However, NHC never at any time forecast Gabrielle to reach hurricane
intensity nor to pose a significant threat to the U. S. coast.
The official TPC/NHC report on Tropical Storm Gabrielle, authored by
Daniel Brown, is now available online on NHC's website. Some of the
information above was taken from this report.
Also, the Wikipedia report on Gabrielle may be found at the following
link:
http://en.wikipedia.org/wiki/Tropical_Storm_Gabrielle_%282007%29
(Report written by Gary Padgett)
HURRICANE HUMBERTO
(TC-09)
12 - 14 September
--------------------------------------
A. Synoptic History
-------------------
A frontal trough moved offshore of southern Florida on 5 September
with the western end moving slowly westward for the next several days,
occasionally producing disorganized thunderstorm activity. By the 11th
the system had reached the northwestern Gulf of Mexico. Early the next
day thunderstorms rapidly increased near the trough and a tropical
depression formed about 105 nm south of Galveston. The depression
became a tropical storm a few hours later as it moved slowly northward
and was named Humberto. The newly-christened cyclone turned slightly
to the north-northeast and continued to rapidly intensify, reaching
hurricane intensity early on 13 September while located about 25 nm
south of High Island, Texas. Hurricane Humberto made landfall just east
of High Island around 0700 UTC at its peak intensity of 80 kts. The
storm then moved over extreme southeastern Texas and southwestern
Louisiana and weakened to a tropical storm at 13/2100 UTC while located
about 120 km west-northwest of Lafayette, Louisiana. The cyclone soon
weakened to a tropical depression near Alexandria, Louisiana, and
dissipated over central Mississippi on the 14th. One fatality is
directly attributable to Humberto and U. S. damage is estimated at
about $50 million.
B. Discussion
-------------
Based on the analyzed Best Track in the official TPC/NHC storm report,
Humberto's MSW climbed from 25 to 80 kts in 24 hrs. This represents the
most rapid intensification on record for a system from below tropical
storm intensity to hurricane force while located so near a coastline.
With a hurricane making landfall when 24 hours earlier there was not
even a tropical depression, it was natural that some criticism would be
leveled at NHC by the media. But it has to be kept in mind that NHC is
chartered to issue warnings on tropical (and subtropical) cyclones, and
said warnings can not be issued when a tropical cyclone does not exist!
It is a fact of nature that sometimes tropical weather systems can form
and intensify with amazing (and frightening) rapidity.
Following is a survey of some Atlantic tropical cyclones which
intensified from below tropical storm intensity to hurricane status
within 24 hours or less. (Note: All the MSW values given below are taken
from the current official Atlantic Best Track file. Some of the values
for older cyclones are subject to be modified during the on-going
re-analysis.)
(1) Storm #3, 26 June 1936 - The first data point in the Best Track is
already of tropical storm intensity. However, assuming that 6 hrs
prior it would have been around 30 kts, this storm intensified from
30 to 65 kts in 12 hrs, and from 30 to 70 kts in 18 hrs. AND, this
late June system formed and strengthened right off the Texas coast
and quickly moved inland.
(2) Cindy, 16 September 1963 - Like the 1936 storm, Cindy developed and
quickly intensified right off the Texas coast and moved inland. The
first data point gives a MSW of 40 kts, but again, assuming 30 kts
for 6 hrs earlier, Cindy intensified from 30 to 70 kts in 18 hrs.
(3) Arlene, 1 August 1963 - Arlene's rapid intensification occurred in
the tropical Atlantic several hundred miles east of the Windward
Islands. This cyclone's MSW jumped from 30 to 70 kts in 18 hrs, and
from 30 to 90 kts in 24 hrs.
(4) Flora, 29 September, 1963 - The developing Flora's intensity rose
from 30 to 70 kts in 18 hrs, and from 30 to 85 kts in 24 hrs while
located a few hundred miles east of Trinidad.
(5) Blanche, 11 August 1969 - While located off the U. S. Eastern Sea-
board, Blanche's MSW jumped from 30 to 75 kts within 12 hrs.
(6) Alberto, 3 June 1982 - Moving from the northwestern Caribbean Sea
past western Cuba into the southeastern Gulf of Mexico, Alberto's
intensity climbed from 30 to 75 kts in 18 hrs, and from 25 to 75 kts
in 24 hrs.
(7) Lorenzo, 27 September 2007 - Coming only a couple weeks after
Humberto, Lorenzo became the second rapidly intensifying Gulf of
Mexico storm for the month of September. Lorenzo's intensity rose
from 30 to 70 kts in 18 hrs while located just off the Mexican
coastline.
(8) Celia, 1 August 1970 - Hurricane Celia, which later devastated the
city of Corpus Christi, Texas, is the poster child for how rapidly
a tropical depression can intensify. While located in the south-
central Gulf of Mexico, Celia's MSW spurted from 30 to 100 kts in
only 18 hrs! The 100-kt MSW at 0000 UTC 2 August was accompanied
by a CP of 965 mb, which matches well. Celia's CP fell from 1007 to
965 mb in 24 hrs, and from 990 to 965 mb in only 6 hrs.
The official TPC/NHC report on Hurricane Humberto, authored by Eric
Blake, is now available online on NHC's website. Some of the information
above was taken from this report.
Also, the Wikipedia report on Humberto may be found at the following
link:
http://en.wikipedia.org/wiki/Hurricane_Humberto_%282007%29
(Report written by Gary Padgett)
TROPICAL STORM INGRID
(TC-08)
12 - 18 September
-----------------------------------------
A. Synoptic History
-------------------
A large tropical wave exited the western coast of Africa on
6 September but ran into strong easterly shear which inhibited
development for several days. On the 9th a broad area of low pressure
developed along the wave axis about midway between Africa and the Lesser
Antilles. Environmental conditions gradually became more favorable as
time wore on and convective activity became persistent near the LOW
center on 11 September. By the early morning of the 12th, when the
LLCC was centered about 975 nm east of the Lesser Antilles, the system
had acquired sufficient organization to be designated as a tropical
depression. The system moved on a general west-northwesterly track
within weak steering flow along the southern periphery of a mid-
tropospheric ridge. Despite moderate vertical wind shear, the
cyclone continued to show improved organization and was upgraded to
Tropical Storm Ingrid during the evening of 13 September while centered
a few hundred miles east of the Lesser Antilles. Ingrid reached its
estimated peak intensity of 40 kts early on the morning of the 14th.
Later that day, shear increased and Ingrid weakened back to depression
status at 1800 UTC 15 September. The strong shear persisted and Ingrid
degenerated to a broad remnant LOW early on the 17th about 140 nm east-
northeast of Antigua.
NOTE: The initial advisories on Tropical Depression 08 (pre-Ingrid) and
Tropical Depression 09 (pre-Humberto) were both issued at the same time:
at 1500 UTC on 12 September. The decision to initiate advisories on the
tropical Atlantic depression had been made early in the morning, and that
system had already been identified as TD-08 on NRL's website before it
was discovered that the Gulf of Mexico system had become a tropical
depression.
B. Discussion
-------------
The primary difference between the analyzed "best track" for Ingrid
and the operational track was the time that the system reached tropical
storm intensity. Operationally, Ingrid was upgraded to tropical storm
status at 14/0300 UTC, but the "best track" backs up the onset of
tropical storm-force winds to 13/0600 UTC. There was a hint in the
NHC discussion for 13/1500 UTC that TD-08 might have briefly been a
tropical storm earlier based on some unflagged 35-kt wind vectors from
QuikScat, but by the 1500 UTC advisory time the satellite signature had
degraded some, suggesting weakening.
The peak intensity for Ingrid in the "best track" has been left at
40 kts, which was the peak operational intensity. This is a little
surprising, given that at 14/1118 UTC the SFMR reported winds of 51 kts
in the southwest quadrant, and concurrent T-numbers from both TAFB and
SAB were T3.0 (45 kts).
Ingrid represented what was, climatologically speaking, the final
candidate of the 2007 hurricane season for an intense hurricane to
threaten populated areas or make landfall in the western portion of the
Atlantic basin. Karen and Melissa formed during the final week of
September, and again from a climatological perspective, had only a low
probability (especially Melissa) of moving all the way across the
Atlantic to threaten or strike the Caribbean islands or the U. S. coast.
The official TPC/NHC report on Tropical Storm Ingrid, authored by
Michelle Mainelli, is now available online on NHC's website.
Also, the Wikipedia report on Ingrid may be found at the following
link:
http://en.wikipedia.org/wiki/Tropical_Storm_Ingrid_%282007%29
(Report written by Gary Padgett)
TROPICAL DEPRESSION
(TC-10)
18 - 22 September
---------------------------------------
A. Synoptic History
-------------------
A decaying frontal boundary became stationary off the southeastern
U. S. coast on 17 September. The next day, an upper-level LOW formed
over Florida and the eastern Gulf of Mexico with a westward-moving
tropical wave moving over the Bahamas. These features combined to
produce a weak area of low-pressure over the western Bahamas later
on the 18th. The system moved slowly westward over Florida and into
the eastern Gulf of Mexico during 19-20 September. On 21 September
convection increased near the surface LOW, and a subtropical depression
formed around 1200 UTC about 40 nm southwest of Apalachicola, Florida.
The depression gained tropical characteristics and was classified as
a tropical depression at 1800 UTC. The estimated MSW never exceeded
30 kts and the depression made landfall around 22/0000 UTC near Fort
Walton Beach, Florida, and dissipated a few hours later. Impacts in
the areas along the path of the depression were minimal.
B. Discussion
-------------
Again, as with Humberto, there was some criticism leveled at NHC for
its seeming slowness in declaring a depression and initiating advisories,
given how close to the coast the system was. At the time of the initial
advisory on Subtropical Depression 10, the center was only about 40 nm
southwest of Apalachicola, Florida, although it was moving away from that
reference point. Emergency Managers in the Florida Panhandle were faced
with a system very near the coast which was forecast to intensify into a
tropical storm and make landfall within 12 to 24 hours.
The issue here is the rather "fuzzy" and subjective definition of a
subtropical depression (or a tropical depression for that matter).
Whereas the tropical (and subtropical) storm category as well as the
hurricane are defined by a minimum wind speed criterion, there is no
such lower MSW bound for the depression category. Factors such as
the depth and amount of convection, organization of the convection,
"tightness" of the circulation, thermal properties, etc all come into
play in deciding whether to "start" a depression or continue to refer
to a system as a low-pressure area (either tropical or non-tropical).
And the process is inherently subjective because some of these criteria
cannot be easily quantified.
In the regular Tropical Weather Outlooks the system was referred to
as a 'weak low-pressure system' on the 19th and 20th. During the
evening of 20 September, after a reconnaissance flight into the LOW,
it was referred to as a 'well-defined low-pressure system', thus
highlighting the increasing organization. Even early on the 21st, it
seems that the degree of convective organization had not yet progressed
to the point that the forecaster felt advisories were warranted.
However, if the system had been upgraded to a depression of either
variety sooner, there would have been more media hype; and given that
it essentially turned out to be a non-event, no doubt NHC would have
then been criticized for "crying wolf". In the author's opinion, NHC
handled this system very well.
The official TPC/NHC report on Tropical Depression 10, authored by
Jamie Rhome, is now available online on NHC's website.
Also, the Wikipedia report on TD-10 may be found at the following
link:
http://en.wikipedia.org/wiki/Tropical_Depression_Ten_%282007%29
(Report written by Gary Padgett)
SUBTROPICAL/TROPICAL STORM JERRY
(TC-11)
20 - 25 September
----------------------------------------------------
A weak non-tropical LOW had formed in the central North Atlantic
roughly half-way between Bermuda and the Azores as early as 20 September.
Over the next few days the LOW drifted eastward. A Tropical Weather
Outlook on the 20th mentioned the system and that it was being monitored
for possible tropical or subtropical development. By the morning of the
22nd the system had become a little better organized, but environmental
conditions were only marginally favorable for development. Advisories
were initiated on Subtropical Depression 11 at 0900 UTC on 23 September,
and the system was upgraded to Subtropical Storm Jerry six hours later.
Jerry at the time was located approximately 925 nm west of the Azores.
The system was treated as a subtropical cyclone since it was well-
involved with an upper-level LOW. Moving slowly northward, Jerry
was reclassified as a tropical storm at 24/0300 UTC as thunderstorm
activity increased near the center. The cyclone never strengthened
above minimal tropical storm intensity of 35 kts, and weakened back
to a depression later on the 24th as it accelerated northeastward
ahead of an approaching cold front.
Tropical Depression Jerry dissipated late on the 24th when it lost
its closed circulation about 700 nm northwest of the Azores. However,
on the final advisory, issued at 25/0300 UTC, Jerry was operationally
re-upgraded to a tropical storm, although the Best Track does not
reflect this since the system no longer had a closed circulation. A
QuikScat pass at 24/2136 UTC had revealed that Jerry's circulation had
opened up into a sharp trough within southwesterly flow ahead of a
large, extratropical LOW. However, as Jerry accelerated during the
evening of the 24th, QuikScat data indicated that winds at the base of
the trough increased to about 40 kts. Presumably as a precaution to
any shipping interests, Jerry underwent an apparent upgrade back to
tropical storm intensity, but the NHC discussion made it plain that the
system was no longer a tropical cyclone. Just an interesting little
vicissitude in the life of what was probably the least-significant
tropical cyclone of 2007.
The official TPC/NHC report on Tropical Storm Jerry, authored by
Lixion Avila, is now available online on NHC's website.
Also, the Wikipedia report on Jerry may be found at the following
link:
http://en.wikipedia.org/wiki/Tropical_Storm_Jerry_%282007%29
(Report written by Gary Padgett)
HURRICANE KAREN
(TC-12)
25 - 30 September
----------------------------------------
A tropical wave departed the west coast of Africa on 21 September
and spawned a large area of disturbed weather. The system gradually
increased in organization and advisories were initiated on Tropical
Depression 12 at 25/0300 UTC with the center located 1475 nm east of
the southern Windward Islands. Six hours later the depression was
upgraded to Tropical Storm Karen. Karen moved west-northwestward
across the tropical Atlantic and strengthened into a minimal hurricane
on the 26th while centered about 1050 nm east of the southern Windward
Islands. However, a little later that day southwesterly wind shear
associated with a sharp upper-level trough caused Karen to begin
weakening. As the shear increased over the next couple of days, the
cyclone continued to lose organization. Karen eventually weakened to
a tropical depression on the 29th and dissipated later that day about
425 nm east of the Leeward Islands. A remnant area of showers and
squalls lingered near and east of the Leewards for a few more days.
Operationally, Karen was treated as a strong tropical storm with a
peak MSW of 60 kts. A NOAA Hurricane Hunter plane investigating Karen
during the evening of the 26th found surface winds of 62 kts. Given
that the storm's satellite signature had degraded significantly from
earlier in the day, it was inferred that Karen had been of minimal
hurricane intensity on the morning of 26 September. A decision was
made during post-season analysis to posthumously upgrade Karen to a
hurricane, making a total of six hurricanes for the 2007 Atlantic
season.
From the beginning of regular operational naming of tropical cyclones
in the Atlantic in 1950 through the year 2002, only one named tropical
storm was upgraded to hurricane status posthumously--Floyd of 1993.
However, Karen is the fourth such hurricane to be upgraded after-the-fact
since 2003, the others being Erika of 2003, Gaston of 2004, and Cindy of
2005. (Note: There were two unnamed hurricanes added to the official
roster of tropical cyclones in 1954 and 1959, and of course there is the
famous unnamed hurricane of 1991 (Perfect Storm), which was deliberately
left unnamed and treated as a non-tropical system operationally in order
not to confuse the public.)
The official TPC/NHC report on Hurricane Karen, authored by Richard
Pasch, is now available online on NHC's website.
Also, the Wikipedia report on Karen may be found at the following
link:
http://en.wikipedia.org/wiki/Hurricane_Karen_%282007%29
(Report written by Gary Padgett)
HURRICANE LORENZO
(TC-13)
25 - 28 September
-------------------------------------
A tropical wave which had crossed the Atlantic and Caribbean Sea
eventually made its way into the southwestern Gulf of Mexico by late
September, spawning a tropical depression on the 25th about 150 nm
east-northeast of Tuxpan, Mexico. Although initially forecast to
strengthen into a tropical storm fairly quickly, Tropical Depression 13
spent a couple of days meandering around the Bay of Campeche without
developing. However, a reconnaissance flight into the depression on
the late morning of 27 September found that the system had strengthened
into a 50-kt tropical storm, which was named Lorenzo. Lorenzo at the
time was located about 115 nm east-southeast of Tuxpan. The cyclone
quickly intensified, reaching hurricane status during the evening of
the 27th. Lorenzo peaked at 70 kts before weakening slightly just prior
to making landfall around 0500 UTC 28 September near Tecolutla--about
65 km southeast of Tuxpan. Once inland the cyclone quickly weakened
and dissipated later that day. The Mexican government reported that
six fatalities were attributable to Hurricane Lorenzo.
Based on the analyzed Best Track, Lorenzo's MSW increased from 30 kts
to 70 kts within an 18-hour period. Operationally, the winds jumped from
30 kts to 65 kts in 12 hours. (See the discussion above in the report
for Hurricane Humberto for further examples of rapidly intensifying
tropical cyclones.) Like Humberto, Lorenzo was very near the coastline
in the western Gulf of Mexico when it underwent rapid intensification
from a tropical depression to a Category 1 hurricane. Other than the
fact that one struck the U. S. while the other struck Mexico, the main
difference was that in the case of Lorenzo, a tropical depression had
been present for two days and had been consistently forecast to intensify
into a tropical storm, whereas in the case of Humberto, no tropical
depression, nor likely even a well-defined LOW, had existed 24 hours
prior to Humberto's landfall as a strong Category 1 hurricane.
The official TPC/NHC report on Hurricane Lorenzo, authored by James
Franklin, is now available online on NHC's website.
Also, the Wikipedia report on Lorenzo may be found at the following
link:
http://en.wikipedia.org/wiki/Hurricane_Lorenzo_%282007%29
(Report written by Gary Padgett)
TROPICAL STORM MELISSA
(TC-14)
28 September - 2 October
--------------------------------------------
Tropical Storm Melissa was the final 2007 tropical cyclone to form
in the deep tropical Atlantic, and like its predecessors Ingrid and
Karen, was another senseless victim of vertical shear. The parent
tropical wave left the coast of Africa on the 26th with an area of low
pressure forming the next day near the Cape Verde Islands. Convection
increased abruptly early on the 28th and the system was classified as a
tropical depression at 28/1500 UTC, centered about 100 nm west-southwest
of the southernmost Cape Verdes. The depression strengthened slightly
while inching westward, and was upgraded to Tropical Storm Melissa at
29/0900 UTC. Melissa maintained tropical storm status for only about a
day, weakening to a depression on 30 September within an environment of
increasing westerly wind shear. The depression accelerated somewhat
toward the west-northwest as convection became intermittent, and later
on the 30th the depression degenerated to a remnant LOW about 475 nm
west of the Cape Verde Islands.
The remnant LOW continued to move west-northwestward for several days
into the central North Atlantic. Convection continued to flare up in
association with the LOW, and Dvorak numbers from SAB briefly increased
to T2.0/2.0 on 1 October. The final reference to the system in a High
Seas Forecast was at 04/0600 UTC, placing the weak LOW near 22N/50W.
However, the official analyzed Best Track for Melissa tracks the remnant
LOW to near 25N/54W at 05/1800 UTC. Operationally, Melissa was carried
as a tropical storm for 30 hours, peaking at 40 kts at 30/0000 UTC. But
in the Best Track, Melissa's tenure as a tropical storm is only 24 hours,
and the peak MSW has been reduced to 35 kts.
The official TPC/NHC report on Tropical Storm Melissa, authored by
Richard Knabb, is now available online on NHC's website.
Also, the Wikipedia report on Melissa may be found at the following
link:
http://en.wikipedia.org/wiki/Tropical_Storm_Melissa_%282007%29
(Report written by Gary Padgett)
*************************************************************************
NORTHEAST PACIFIC (NEP) - North Pacific Ocean East of Longitude 180
Activity for September: 1 tropical depression
1 tropical storm
2 hurricanes **
** - one of these formed in August and was covered in the August summary
NOTE!!! The Northeast Pacific basin will be covered in the second
installment of the September summary.
*************************************************************************
NORTHWEST PACIFIC (NWP) - North Pacific Ocean West of Longitude 180
Activity for September: 3 tropical depressions **
3 tropical storms
2 typhoons ++
1 super typhoon
** - two of these classified as tropical depressions by JMA only
++ - one of these formed in August and was covered in the August summary
NOTE!!! The Northwest Pacific basin will be covered in the third
installment of the September summary.
*************************************************************************
NORTH INDIAN OCEAN (NIO) - Bay of Bengal and Arabian Sea
Activity for September: 1 depression **
** - no warnings issued on this system by JTWC
NOTE!!! The North Indian Ocean basin will be covered in the second
installment of the September summary.
*************************************************************************
SOUTHWEST INDIAN OCEAN (SWI) - South Indian Ocean West of Longitude 90E
Activity for September: No tropical cyclones
*************************************************************************
NORTHWEST AUSTRALIA/SOUTHEAST INDIAN OCEAN (AUW) - From 90E to 135E
Activity for September: No tropical cyclones
*************************************************************************
NORTHEAST AUSTRALIA/CORAL SEA (AUE) - From 135E to 160E
Activity for September: No tropical cyclones
*************************************************************************
SOUTH PACIFIC (SPA) - South Pacific Ocean East of Longitude 160E
Activity for September: No tropical cyclones
*************************************************************************
SPECIAL FEATURE - SOURCES OF TROPICAL CYCLONE INFORMATION
The purpose of this section is to list some websites where many and
varied types of tropical cyclone information are archived. Many readers
will know about these already, but for the benefit of those who don't,
I wanted to include them.
(1) Aircraft Reconnaissance Information
---------------------------------------
Various types of messages from reconnaissance aircraft may be
retrieved from the following FTP site:
ftp://ftp.nhc.noaa.gov/pub/products/nhc/recon/
Information regarding how to interpret the coded reconnaissance
messages may be found at the following URL:
http://www.nhc.noaa.gov/reconlist.shtml
Links are also included to websites with further information about the
U. S. Air Force 53rd Weather Reconnaissance Squadron and the NOAA Air-
craft Operations Center.
(2) Archived Advisories
-----------------------
All the advisory products (public advisories, forecast/advisories,
strike probabilities, discussions, various graphics) issued by TPC/NHC
are archived on TPC's website. For the current year (using 2004 as an
example), the archived products can be found at:
http://www.nhc.noaa.gov/archive/2004/index.shtml
Links to tropical products archives for earlier years are available at
the following URL:
http://www.nhc.noaa.gov/pastall.shtml
JTWC warnings for past storms are archived on the NRL Monterrey website:
http://www.nrlmry.navy.mil/tc_pages/tc_home.html
On the NRL site, the link to past years can be found in the upper left
corner of the screen.
I am not aware at the moment of any other TCWC which archives all
its tropical cyclone warning/advisory products for public access, but
if I learn of any, I will add them to this list.
(3) Satellite Imagery
---------------------
Satellite images of tropical cyclones in various sensor bands are
available on the NRL Monterrey and University of Wisconsin websites,
courtesy of Jeff Hawkins and Chris Velden and their associates. The
links are:
http://www.nrlmry.navy.mil/tc_pages/tc_home.html
http://cimss.ssec.wisc.edu/tropic/tropic.html
On the NRL site, the link to past years can be found in the upper left
corner of the screen. For the CIMSS site, a link to data archives is
located in the lower left portion of the screen.
Additional tropical satellite imagery, along with looping ability for
composite microwave imagery for the Western Hemisphere north of the
equator, can be found at:
(1) For the Eastern North Pacific:
http://www.ssd.noaa.gov/PS/TROP/trop-epac.html
(2) For the Atlantic, Gulf of Mexico and Caribbean Sea:
http://www.ssd.noaa.gov/PS/TROP/trop-atl.html
(4) Cyclone Tracking Information
--------------------------------
There is a U. S. Navy site that tracks tropical cyclones at 6-hourly
intervals which often includes pre and post-advisory positions. The
link to the site is:
http://www.nrlmry.navy.mil/atcf_web/doc_archives/
Steve Young has compiled many of these tracks onto a single webpage
which is very user-friendly:
http://home.earthlink.net/~shy9/tc1.htm
I'm sure there are other sites with available imagery available, and
as I learn of them, I will add the links to this list.
*************************************************************************
EXTRA FEATURE
In order to shorten the amount of typing in preparing the narrative
material, I have been in the habit of freely using abbreviations and
acronyms. I have tried to define most of these with the first usage
in a given summary, but I may have missed one now and then. Most of
these are probably understood by a majority of readers but perhaps a
few aren't clear to some. To remedy this I developed a Glossary of
Abbreviations and Acronyms which I first included in the August, 1998
summary. I don't normally include the Glossary in most months in
order to help keep them from being too long. If anyone would like to
receive a copy of the Glossary, please e-mail me and I'll be happy
to send them a copy.
*************************************************************************
AUTHOR'S NOTE: This summary should be considered a very preliminary
overview of the tropical cyclones that occur in each month. The cyclone
tracks (provided separately) will generally be based upon operational
warnings issued by the various tropical cyclone warning centers. The
information contained therein may differ somewhat from the tracking and
intensity information obtained from a "best-track" file which is based
on a detailed post-seasonal analysis of all available data. Information
on where to find official "best-track" files from the various warning
centers will be passed along from time to time.
The track files are not being sent via e-mail. They can be retrieved
from the archive sites listed below. (Note: I do have a limited e-mail
distribution list for the track files. If anyone wishes to receive
these via e-mail, please send me a message.)
Both the summaries and the track files are standard text files
created in DOS editor. Download to disk and use a viewer such as
Notepad or DOS editor to view the files.
The first summary in this series covered the month of October,
1997. Back issues can be obtained from the following websites
(courtesy of Michael Bath, Michael V. Padua, Michael Pitt, Chris
Landsea, and John Diebolt):
http://australiasevereweather.com/cyclones/
http://www.typhoon2000.ph <http://www.typhoon2000.ph/>
http://mpittweather.com <http://mpittweather.com/>
ftp://ftp.aoml.noaa.gov/hrd/pub/landsea/padgett/
http://www.tropicalcyclone2005.com/
Another website where much information about tropical cyclones may
be found is the website for the UK Meteorological Office. Their site
contains a lot of statistical information about tropical cyclones
globally on a monthly basis. The URL is:
http://www.metoffice.gov.uk/weather/tropicalcyclone
TROPICAL CYCLONE REPORTS AVAILABLE
JTWC now has available on its website the Annual Tropical Cyclone
Report (ATCR) for 2005 (2004-2005 season for the Southern Hemisphere).
ATCRs for earlier years are available also.
The URL is: http://metocph.nmci.navy.mil/jtwc.php
Also, TPC/NHC has available on its webpage nice "technicolor"
tracking charts for the 2006 Atlantic and Eastern North Pacific
tropical cyclones; also, storm reports for all the 2006 Atlantic
and Eastern North Pacific cyclones are now available, as well as
track charts and reports on storms from earlier years.
The URL is: http://www.nhc.noaa.gov <http://www.nhc.noaa.gov/>
A special thanks to Michael Bath of McLeans Ridges, New South Wales,
Australia, for assisting me with proofreading the summaries.
PREPARED BY
Gary Padgett
E-mail: garyp@alaweb.com
Phone: 334-222-5327
Kevin Boyle (Northwest Pacific)
E-mail: newchapelobservatory@btinternet.com
Simon Clarke (Northeast Australia/Coral Sea, South Pacific)
E-mail: scla4255@bigpond.net.au
*************************************************************************
*************************************************************************
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