African wave 99L may develop; Felicia threatens Hawaii; record rains from Morakot

By: Dr. Jeff Masters , 3:20 PM GMT on August 09, 2009

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A strong tropical wave with a high amount of spin moved off the coast of Africa yesterday, and has a good chance of becoming the first named storm of the 2009 Atlantic hurricane season. The wave was designated 99L by NHC Sunday morning. Wind shear is moderate, about 10 knots, and sea surface temperatures are moderately warm, about 27 - 28°C. There is a large area of dry air to 99L's north, but this is not currently interfering with the storm's organization. This morning's QuikSCAT pass showed a nearly closed surface circulation, stretched out along two axes. The storm can now be classified as tropical depression using the satellite-based Dvorak classification technique, but the surface circulation will have to show better definition before 99L can be classified as a tropical depression. Top winds were in the 20 - 30 mph range, as estimated by QuikSCAT and the Dvorak satellite estimates.


Figure 2. Visible satellite image of disturbance 99L.

Wind shear is expected to be low, 5 - 10 knots, tonight through Tuesday. SSTs will remain relatively constant at 27°C, so conditions favor development. NHC has given 99L a moderate (30 - 50% chance) of developing into a tropical depression by Tuesday morning, which is a reasonable forecast. The UKMET, GFS, and NOGAPS models all develop 99L into a tropical depression 1 - 4 days from now. The dry air of the Saharan Air Layer may become a problem for 99L 2 -4 days from now, as the storm moves slightly north of due west. It is too early to say if 99L will recurve north of the Lesser Antilles Islands or not, since it will be at least 6 days before the storm makes it that far.

The GFS model predicts development of a new tropical wave coming off the coast of Africa about 6 - 7 days from now.

Felicia weakens to a tropical storm, still a threat to Hawaii
Tropical Storm Felicia has weakened steadily over the past 24 hours, thanks to cool sea surface temperatures and increasing shear. Recent satellite imagery shows that wind shear is beginning to affect the storm, with strong upper-level winds from the west pushing the storm's heavy thunderstorm activity all to the east side of the center.


Figure 2. History of hurricane activity over Hawaii since 1950. Hawaii islands have been hit by only 9 tropical cyclones of tropical depression or greater strength, with 4 others passing withing 75 miles of an island. Image credit: NOAA Coastal Services Center.

Sea surface temperatures (SSTs) under Felicia are 25°C, well below the 26°C threshold typically needed to sustain a hurricane. SSTs will slowly increase to 26°C by the time the storm reaches Hawaii, though. Wind shear has increased to a moderate to high 20 knots, and is expected to increase further to 30 knots by Monday morning. The high shear combined with the cool SSTs should reduce Felicia to tropical depression strength by the time the center reaches the Hawaiian Islands Monday night. The wind speed probabilities forecast shows about a 40% chance Felicia will still be a weak tropical storm when it moves through the islands Monday night, and 40% chance it will be a tropical depression. If Felicia does hold together that long, it would be only the tenth tropical cyclone of tropical depression or higher strength to affect the islands since 1950 (Figure 1). Large swells from Felicia are already affecting the Big Island, and a high surf warning has been posted for the Big Island. Felicia or its remnants should bring heavy rain, flash flooding, and mud slides to the islands beginning Monday morning, and a Flash Flood Watch has been posted for most of the islands.

Typhoon Morakot hits China
Typhoon Morakot hit China this morning as a tropical storm, lashing the mainland with very heavy rain. Yesterday, Morakot hit Taiwan, dumping up to 80 inches of rain on the island over a 2-day period, according to news reports. The world 2-day rainfall record is 98.42", set at Reunion Island on March 15 - 17, 1952, so the Typhoon Morakot 2-day totals are some of the highest ever measured in the world. The highest 1-day rainfall total ever recorded on Taiwan occurred Saturday at Weiliao Mountain in Pingtung County, which recorded 1.403 meters (4.6 feet or 55 inches) or rain. Nine the ten highest one-day rainfall amounts in Taiwanese history were reached on Saturday, according to the Central Weather Bureau. Three are dead and 31 people missing on the island, and Morakot also killed 23 people in the Philippines.

I'll have an update on Monday.

Jeff Masters

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Quoting Acemmett90:
Is this just dissipated i would laugh


I am pretty sure this will not dissipate.
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currently maximum sustained winds with 99L are 31mph pressure is 1010mb and the wind radius of 31mph is 35 miles, there is no reason for this not to be a TD at 2 o'clock
Quoting futuremet:
12Z CMC


In agreement with the NOGAPS
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Quoting futuremet:
12Z CMC


West!
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Low level spiral bands:
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got to tighen up a little more then it gets 4 more points which will bring total to 41 then T.C.F.A.has got to be issued as per guidance
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421. Relix
The tracking of future Ana should be very fun. Also, strong wave behind it. Its a cluster... but has potential.
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12Z CMC
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Quoting Stormchaser2007:


Thats very unlikely. Maybe 3-4. Another 4 in September then things shut down in late September.


why do things shut down in September? I have been hearing this from so many on here.

El Nino will not be strong enough to shut down the season in September like what happened in some other years. StormW has touched on that before as well.

I feel we will see 2 or 3 systems in October as well.
12:30 EDT:
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Quoting Intimidator3:


Clear your temp internet files and cookies, close all browser windows, and come back. Should take care of it :)


I just refresh again and it usually comes up. Also firefox seems to work better with the size of the blog (meaning page length and number of photos posted) than other browsers I've tried. YMMV
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Quoting sammywammybamy:


6-8


Thats very unlikely. Maybe 3-4. Another 4 in September then things shut down in late September.
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awesome.
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Quoting KEEPEROFTHEGATE:
not fully but soon
no it is completely closed as stated by the NHC
Quoting Acemmett90:

im gettting it ever time and im getting the
JeffMasters's WunderBlog
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Clear your temp internet files and cookies, close all browser windows, and come back. Should take care of it :)
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Quoting sammywammybamy:



Do you think the direct wave after Ana will also have chance to develop... Look at its bright convection....

I am talking about wave # 2


Im not sure. I dont see signs of a circulation like wave 3 has. Just some pretty cold convection. Although thats usually the precursor to a circulation.
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Quoting Stormchaser2007:


It does have a closed surface circulation.
not fully but soon
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Quoting ackee:
how many storms u guys think we see for the month of AUG
4 or more
Rock solid consensus.

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Quoting Stormchaser2007:
KOTG

You may want to do a recount.

TROPICAL WAVE IS ALONG 20W/21W S OF 18N MOVING W 15-20 KT.
LATEST VISIBLE SATELLITE IMAGERY INDICATES THE WELL DEFINED
LOW/MID LEVEL CYCLONIC CIRCULATION CENTER
MOVING JUST E OF THE
WAVE AXIS. THE WAVE AXIS IS EMBEDDED WITHIN THE MOISTURE MAXIMUM
OBSERVED IN TOTAL PRECIPITABLE WATER IMAGERY. CLUSTERS OF
SCATTERED MODERATE TO ISOLATED STRONG CONVECTION ARE ASSOCIATED
WITH THE LOW/MID LEVEL CIRCULATION COVERING THE AREA FROM
9N-16N BETWEEN 19W-24W.



The NHC says it's well defined.
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Quoting weatherwatcher12:

ADD UP THE POINTS.
1.)? If value is 35 to 38, TCFA may be required depending on? Dvorak trends (i.e. MET T-# and 24 hr change).
2.)? If value is 39 or >, a TCFA should be issued.
* In most situations, (i.e. organized convection for at least 12 hrs, >25 kts sfc wind detected), NHC will go directly to advisory issuance!
NAVMARFCSTCEN/NHC POC: LT Roberts 786-556-1702
actually if it is higher than 38 it has to be posted
400. ackee
how many storms u guys think we see for the month of AUG
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Wow

MPE

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Quoting Dakster:


There is a 2pm regular advisory... Right?


TWD ya.
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Quoting naplesdreamer28:
the blog is already overloading! I'm getting occassional blank white pages when refreshing.
ive been getting it since yesterday
Quoting Drakoen:


Looks odd.
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Quoting canesrule1:
T.C.F.A Point Chart:
Surface
Condition Points
A circulation is evident using visible satellite, shortwave infrared, microwave imagery or QuikSCAT/Windsat ambiguities
3 points
A circulation has been evident for at least 24 hours
5 points
A westerly surface- or gradient-level wind of 5 kt that is within 200 nm (370 km, 230 mi) south of the centre of the disturbance
5 points
Any wind associated with the system is at least 20 kt
2 points
Any wind associated with the system is at least 25 kt
3 points
Any wind associated with the system is at least 30 kt
4 points
A weather station within 200 nm of the system has reported had a pressure drop of 2 mb over 24 hours
3 points
A weather station within 200 nm of the system has had a pressure drop of 3 mb over 24 hours
4 points
The estimated MSLP of the system is less than 1010 to 1009 mb
3 points
The estimated MSLP of the system is 1008 mb or less
4 points

[edit] 500 mb height
Condition Points
There is evidence of at least an inverted trough
2 points
There is evidence of a closed circulation in the system
4 points

[edit] 200 mb height
Condition Points
Westerly flow of at least 15 kt over the disturbance
-4 points
There is evidence of anticyclonic outflow over the centre of the disturbance
4 points
Easterly flow of at most 20 kt over the disturbance
3 points

[edit] Sea surface temperature
Condition Points
The sea surface temperature is 26 Celsius (78.8 Fahrenheit) or higher
3 points

[edit] Satellite data
Condition Points
The system has persisted for at least 24 hours
3 points
The system has persisted for at least 48 hours
4 points
The system has persisted for at least 72 hours
5 points
The system has a Dvorak classification of T1.0 to T1.5 from all three agencies (TAFB, SAB, AFWA)
3 points
The system has a Dvorak classification of T1.5 to T2.0 from all three agencies
5 points
The Dvorak final-T number has decreased by T0.5 to T1.0 from two or more agencies
-2 points

[edit] Miscellaneous
Condition Points
The cloud system is north (or south) of 5 degrees latitude
3 points
The tropical system is within 72 hours of reaching a Department of Defense resource
3 points
The cloud system center and the satellite centre fixes for the system are within 2 degrees of each other
2 points

ADD UP THE POINTS.
1.)? If value is 35 to 38, TCFA may be required depending on? Dvorak trends (i.e. MET T-# and 24 hr change).
2.)? If value is 39 or >, a TCFA should be issued.
* In most situations, (i.e. organized convection for at least 12 hrs, >25 kts sfc wind detected), NHC will go directly to advisory issuance!
NAVMARFCSTCEN/NHC POC: LT Roberts 786-556-1702
Member Since: May 16, 2009 Posts: 1 Comments: 1231
Possible new TD in EPAC:


Otherwise I expect a red at the 2pm advisory for the African Wave.
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Quoting extreme236:


Very doubtful they would issue a special advisory for this.


There is a 2pm regular advisory... Right?
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Quoting sammywammybamy:
And the Best Pinhole Eye Award goes to : Hurricane Gilbert...



Wilma had a 2 nm wide eye.There are F5 Tornado's that where bigger than Wilma's eye. It goes to Wilma hands down.
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KOTG

You may want to do a recount.

TROPICAL WAVE IS ALONG 20W/21W S OF 18N MOVING W 15-20 KT.
LATEST VISIBLE SATELLITE IMAGERY INDICATES THE WELL DEFINED
LOW/MID LEVEL CYCLONIC CIRCULATION CENTER
MOVING JUST E OF THE
WAVE AXIS. THE WAVE AXIS IS EMBEDDED WITHIN THE MOISTURE MAXIMUM
OBSERVED IN TOTAL PRECIPITABLE WATER IMAGERY. CLUSTERS OF
SCATTERED MODERATE TO ISOLATED STRONG CONVECTION ARE ASSOCIATED
WITH THE LOW/MID LEVEL CIRCULATION COVERING THE AREA FROM
9N-16N BETWEEN 19W-24W.

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Quoting IKE:


Odds are it never bothers a land-mass....
Yea early this morning the blog was talking about Bill now we are already to Claudette. It just floors me!
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T.C.F.A Point Chart:
Surface
Condition Points
A circulation is evident using visible satellite, shortwave infrared, microwave imagery or QuikSCAT/Windsat ambiguities
3 points
A circulation has been evident for at least 24 hours
5 points
A westerly surface- or gradient-level wind of 5 kt that is within 200 nm (370 km, 230 mi) south of the centre of the disturbance
5 points
Any wind associated with the system is at least 20 kt
2 points
Any wind associated with the system is at least 25 kt
3 points
Any wind associated with the system is at least 30 kt
4 points
A weather station within 200 nm of the system has reported had a pressure drop of 2 mb over 24 hours
3 points
A weather station within 200 nm of the system has had a pressure drop of 3 mb over 24 hours
4 points
The estimated MSLP of the system is less than 1010 to 1009 mb
3 points
The estimated MSLP of the system is 1008 mb or less
4 points

[edit] 500 mb height
Condition Points
There is evidence of at least an inverted trough
2 points
There is evidence of a closed circulation in the system
4 points

[edit] 200 mb height
Condition Points
Westerly flow of at least 15 kt over the disturbance
-4 points
There is evidence of anticyclonic outflow over the centre of the disturbance
4 points
Easterly flow of at most 20 kt over the disturbance
3 points

[edit] Sea surface temperature
Condition Points
The sea surface temperature is 26 Celsius (78.8 Fahrenheit) or higher
3 points

[edit] Satellite data
Condition Points
The system has persisted for at least 24 hours
3 points
The system has persisted for at least 48 hours
4 points
The system has persisted for at least 72 hours
5 points
The system has a Dvorak classification of T1.0 to T1.5 from all three agencies (TAFB, SAB, AFWA)
3 points
The system has a Dvorak classification of T1.5 to T2.0 from all three agencies
5 points
The Dvorak final-T number has decreased by T0.5 to T1.0 from two or more agencies
-2 points

[edit] Miscellaneous
Condition Points
The cloud system is north (or south) of 5 degrees latitude
3 points
The tropical system is within 72 hours of reaching a Department of Defense resource
3 points
The cloud system center and the satellite centre fixes for the system are within 2 degrees of each other
2 points
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Quoting extreme236:


Very doubtful they would issue a special advisory for this.


Same.

They would wait until later tonight if anything.
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That pretty much spells out the next 2-3 weeks for the Atlantic Basin.
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Quoting Dakster:
1 hour and counting till the 2pm update... I say they skip red and go to TD.


Very doubtful they would issue a special advisory for this.
Member Since: August 2, 2007 Posts: 19 Comments: 19234
the blog is already overloading! I'm getting occassional blank white pages when refreshing.
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Jeff co-founded the Weather Underground in 1995 while working on his Ph.D. He flew with the NOAA Hurricane Hunters from 1986-1990.

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