Disturbance 90L close to tropical depression strength; TD 2 may rise again

By: Dr. Jeff Masters , 2:02 PM GMT on August 14, 2009

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A strong tropical wave (90L), with a large circulation and a moderate amount of heavy thunderstorm activity, is a few hundred miles southwest of the Cape Verdes Islands, off the coast of Africa. This morning's QuikSCAT pass shows that 90L has a large circulation, but this circulation is not yet well-formed, as it is elongated along an east-west axis. Satellite imagery from the European METEOSAT satellite show that the heavy thunderstorms associated with 90L are gradually becoming better organized, with some spiral banding evident on the south side of the storm. Satellite intensity estimates from NOAA already put 90L at tropical depression strength with 30 mph winds, but the storm does not yet have a well enough formed circulation to be classified as a depression. Water vapor imagery shows that since 90L is forming several hundred miles south of the dry air of the Saharan Air Layer (SAL), the storm should not be affected by dry air and dust as much as Tropical Depression Two was. However, there is some dry air from the SAL being sucked into the circulation of 90L, and this is retarding its development.

Wind shear is moderate, about 10 - 15 knots, but is forecast to fall to the low range, 5 - 10 knots, later today. Shear is then forecast to remain low for the next five days. Sea Surface Temperatures are about 28°C, and will remain in the 27 - 28°C range the next five days. The combination of low wind shear and sufficiently warm SSTs should allow 90L to develop into a tropical depression by Saturday, and potentially reach hurricane strength by Wednesday. Most of our reliable models strengthen 90L into a hurricane by Wednesday, when the storm is expected to be near the northern Lesser Antilles Islands. One important outlier is the ECMWF model, which has 90L passing to the north of the islands, and eventually recurving out to sea east of Bermuda. The ECMWF was by far the most reliable model for forecasting hurricane tracks last year. However, all of our models are pretty unreliable going out 5 days in advance for systems that have yet to reach tropical depression strength. Once 90L becomes a tropical depression and develops a well-formed circulation, the models will have a better handle on forecasting where it will go.


Figure 1. The remnants of Tropical Depression Two (left side of image) and tropical wave 90L (right side of image).

Tropical Depression Two may come back
Tropical Depression Two died yesterday, but may rise again. Satellite loops of the remnants of the storm show that heavy thunderstorms are again attempting a comeback near the axis of what is now a tropical wave. However, dry air continues to interfere with the development of the thunderstorm activity, and moderately high wind shear of 15 - 20 knots is also inhibiting the process. Wind shear over the remnants of TD 2 is expected to remain in the moderate range, 10 - 20 knots, over the next four days. Sea Surface Temperatures (SSTs) are 27°C, but will warm to 28°C two days from now. There is plenty of dry, stable air from the Saharan Air Layer (SAL) to the north and west that will continue to cause the storm problems. The relatively cool SSTs and dry air mean that any re-development of the storm will be slow to occur. NHC has given the system a medium (30 - 50% chance) of becoming a tropical depression again by Sunday morning. Only one reliable model, the NOGAPS, is predicting regeneration of TD 2. The NOAA Hurricane Hunters are flying research missions into the remnants of TD 2 today and Saturday.

I'll have an update Saturday morning, or earlier, if significant developments occur.

Jeff Masters

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Weather456
What do you think of the blob behind 90L

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I posted about this earleir but here it is again. Ex TD2 has been coming under increasing shear from a digging ULL to the N. Shear is now 20 knots cutting across the top of it with more to come.

Here is the shear tendency map. It has been increasing all day in the path of Ex TD2. Click on the shear amp and you will see how the 20 and 30 knots of shear is coming down from the N.



Member Since: August 19, 2006 Posts: 0 Comments: 15816
3581. Walshy
TD2 is on weatherunderground.
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Hello Everyone from St. Croix,

I'am looking at these two storm out in the Atlantic and seem relentless in giving up. Former TD2 is trying to get its act together and it seems better organized since the NHC called it off. TD2 looks like it will make a come back but not for long. I think there is a lot of dry air to the west and north of the system. The dry air is slowing down any significant development. This worries me because a weak storm tends to travel more westward and north west. I hope this thing to sneak by past 60w and sunddenlly goes wild on us. Our 90L system out there is getting really bigger and stronger and computer models is calling for a near or direct hit to the US Virgin Islands. I hope this is not another Omar or Hugo. God save us.
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This run looks either fishy or maybe a New England event.
Member Since: July 1, 2008 Posts: 13 Comments: 7387
00
WTNT32 KNHC 150425
TCPAT2
BULLETIN
TROPICAL DEPRESSION TWO SPECIAL ADVISORY NUMBER 12
NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL AL022009
1230 AM AST SAT AUG 15 2009

...TROPICAL DEPRESSION TWO REGENERATES OVER THE TROPICAL ATLANTIC
OCEAN...

INTERESTS IN THE NORTHERN LEEWARD ISLANDS SHOULD MONITOR THE
PROGRESS OF TROPICAL DEPRESSION TWO.

AT 1230 AM AST...0430 UTC...THE CENTER OF TROPICAL DEPRESSION TWO
WAS LOCATED NEAR LATITUDE 14.6 NORTH...LONGITUDE 45.8 WEST OR ABOUT
1075 MILES...1735 KM...EAST OF THE LEEWARD ISLANDS.

THE DEPRESSION IS MOVING TOWARD THE WEST NEAR 15 MPH...24 KM/HR...
AND THIS GENERAL MOTION WITH A GRADUAL TURN TOWARD THE
WEST-NORTHWEST IS EXPECTED OVER THE NEXT COUPLE OF DAYS.

MAXIMUM SUSTAINED WINDS ARE NEAR 35 MPH...55 KM/HR...WITH HIGHER
GUSTS. SOME STRENGTHENING IS FORECAST DURING THE NEXT 24 HOURS AND
THE DEPRESSION COULD BECOME A TROPICAL STORM THIS WEEKEND.

THE ESTIMATED MINIMUM CENTRAL PRESSURE BASED ON NOAA BUOY 41041 IS
1005 MB...29.68 INCHES.

...SUMMARY OF 1230 AM AST INFORMATION...
LOCATION...14.6N 45.8W
MAXIMUM SUSTAINED WINDS...35 MPH
PRESENT MOVEMENT...WEST OR 270 DEGREES AT 15 MPH
MINIMUM CENTRAL PRESSURE...1005 MB

THE NEXT ADVISORY WILL BE ISSUED BY THE NATIONAL HURRICANE CENTER AT
500 AM AST.

$$
FORECASTER BLAKE/BRENNAN

Member Since: August 10, 2009 Posts: 3 Comments: 672
3577. KEEPEROFTHEGATE (Mod)
Quoting Weather456:
In 1 week, the GFS shows another area right behind 90L, what an onslaught.
3 storms will bloom by the next full moon which is sept 4 then 3 or 4 more as the moon goes new late sept then the window gets closed till mid oct with 1 or 2 late one's to finish up nov
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3576. JRRP
Quoting reedzone:


and much weaker.. interesting

yes
strong TS or weak Cat 1
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TD 2 on NHC page.
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3572. ackee
TD#2IS BACK offical now
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3571. Patrap
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Quoting philliesrock:
GFS is farther north than previous runs. Florida/east coast looks to be in danger this run.

At 168 hours, still looks like Fl straits. Motion just north of west.

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00z GFS has it gunning for SOFLA at 162h...remember the exact track is not the most important thing this far out. It can and will change back and forth.
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In 1 week, the GFS shows another area right behind 90L, what an onslaught.

I does not seem any bit weaker

Member Since: July 24, 2005 Posts: 407 Comments: 19076
Big changes this run
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3566. sfla82
Quoting reedzone:


Like I said earlier.. I'm still holding strong on an East Coast event.


Yeah, I think so too which isn't good news for NC and the northeast!
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Quoting kanc2001:


Hugo


no, no more like Hugo here... I just bought a new house!!
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Quoting JRRP:
more north

126


and much weaker.. interesting
Member Since: July 1, 2008 Posts: 13 Comments: 7387
It is back a little further north than the last run
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Western North Atlantic GFS 00 (so far)
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3561. JRRP
more north

126
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does somebody have the latest gfs run?
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Ex-TD2 looks to be losing some of its convection/thunderstorms (intensity at least)... it needs to take advantage of the current environment or else it won't redevelop (at least not tomorrow).
Member Since: July 6, 2005 Posts: 5 Comments: 580
Member Since: July 24, 2005 Posts: 407 Comments: 19076
3557. KEEPEROFTHEGATE (Mod)
Quoting Tazmanian:
TD 2 is back


000
WHXX01 KWBC 150145
CHGHUR
TROPICAL CYCLONE GUIDANCE MESSAGE
NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL
0145 UTC SAT AUG 15 2009

DISCLAIMER...NUMERICAL MODELS ARE SUBJECT TO LARGE ERRORS.
PLEASE REFER TO NHC OFFICIAL FORECASTS FOR TROPICAL CYCLONE
AND SUBTROPICAL CYCLONE INFORMATION.

ATLANTIC OBJECTIVE AIDS FOR

TROPICAL CYCLONE TWO (AL022009) 20090815 0000 UTC

...00 HRS... ...12 HRS... ...24 HRS. .. ...36 HRS...
090815 0000 090815 1200 090816 0000 090816 1200

LAT LON LAT LON LAT LON LAT LON
BAMS 14.5N 44.8W 14.9N 46.9W 15.9N 49.8W 17.5N 53.9W
BAMD 14.5N 44.8W 15.3N 47.1W 16.4N 49.8W 17.6N 53.0W
BAMM 14.5N 44.8W 15.0N 47.0W 15.9N 49.6W 16.8N 53.1W
LBAR 14.5N 44.8W 15.0N 47.5W 15.8N 50.5W 16.7N 54.0W
SHIP 25KTS 28KTS 32KTS 36KTS
DSHP 25KTS 28KTS 32KTS 36KTS

...48 HRS... ...72 HRS... ...96 HRS. .. ..120 HRS...
090817 0000 090818 0000 090819 0000 090820 0000

LAT LON LAT LON LAT LON LAT LON
BAMS 19.4N 58.2W 23.2N 66.9W 26.7N 73.0W 28.9N 75.6W
BAMD 18.8N 56.5W 21.0N 63.9W 23.5N 70.0W 24.9N 73.6W
BAMM 17.8N 56.9W 19.9N 65.1W 22.2N 72.5W 24.0N 77.7W
LBAR 17.7N 57.7W 20.2N 65.5W .0N .0W .0N .0W
SHIP 41KTS 50KTS 54KTS 59KTS
DSHP 41KTS 50KTS 54KTS 59KTS

...INITIAL CONDITIONS...
LATCUR = 14.5N LONCUR = 44.8W DIRCUR = 270DEG SPDCUR = 14KT
LATM12 = 14.6N LONM12 = 41.7W DIRM12 = 276DEG SPDM12 = 15KT
LATM24 = 14.3N LONM24 = 39.2W
WNDCUR = 25KT RMAXWD = 40NM WNDM12 = 25KT
CENPRS = 1007MB OUTPRS = 1010MB OUTRAD = 150NM SDEPTH = M
RD34NE = 0NM RD34SE = 0NM RD34SW = 0NM RD34NW = 0NM

thats in my blog taz been up for a while navy also has former 02l as a rename inv 91L

2009 Storms
Active Year


Atlantic
91L.INVEST
90L.INVEST
02L.TWO

East Pacific
10E.GUILLERMO
09E.NINE

Central Pacific

West Pacific
94W.INVEST
91W.INVEST
01C.MAKA

Indian Ocean

Southern Hemisphere
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Quoting KEEPEROFTHEGATE:
I did not think anyone else notice that your one of the sharper tools in the shed i see


Thanks !. The 12 , 24 and 48 hr intervals are fairly clear
Member Since: August 19, 2006 Posts: 0 Comments: 15816
14.357 N 46.008 W Wind Direction (WDIR): N ( 350 deg true )
Wind Speed (WSPD): 19.4 kts
Wind Gust (GST): 21.4 kts
Wave Height (WVHT): 7.9 ft
Dominant Wave Period (DPD): 8 sec
Average Period (APD): 5.6 sec
Atmospheric Pressure (PRES): 29.72 in
Pressure Tendency (PTDY): -0.13 in ( Falling Rapidly )
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Quoting philliesrock:
GFS is farther north than previous runs. Florida/east coast looks to be in danger this run.


Like I said earlier.. I'm still holding strong on an East Coast event.
Member Since: July 1, 2008 Posts: 13 Comments: 7387

TD2

90L

AOI

AOI
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3551. 7544
Quoting philliesrock:
GFS is farther north than previous runs. Florida/east coast looks to be in danger this run.


yeap this run might be the bulls eye
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GFS is farther north than previous runs. Florida/east coast looks to be in danger this run.
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Quoting TampaSpin:
Looks like the GFS has TD2 becoming a very strong cane in front of 90L



nope

Td 2 dies

90L intensifies

and a new wave develops behind
Member Since: July 24, 2005 Posts: 407 Comments: 19076
3548. KEEPEROFTHEGATE (Mod)
Quoting kmanislander:


GFS loses ex TD2. The cane is 90L with a new low behind it
I did not think anyone else notice that your one of the sharper tools in the shed i see
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Does anyone think chances for developement above Cuba is higher than a low chance of developing right now?
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OK... have looked at the 00 GFS runs


Is my reading correct that:

a. This is first run including the NOAA Aircraft data?

b. This run of the GFS "drops" exTD2 (ie says that exTD2 will dissipate)?

Thanks
CRS

[edit] the model graphic I am looking at is at:

http://www.nco.ncep.noaa.gov/pmb/nwprod/analysis/carib/gfs/00/index_ten_s_loop.shtml
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TD 2 is back


000
WHXX01 KWBC 150145
CHGHUR
TROPICAL CYCLONE GUIDANCE MESSAGE
NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL
0145 UTC SAT AUG 15 2009

DISCLAIMER...NUMERICAL MODELS ARE SUBJECT TO LARGE ERRORS.
PLEASE REFER TO NHC OFFICIAL FORECASTS FOR TROPICAL CYCLONE
AND SUBTROPICAL CYCLONE INFORMATION.

ATLANTIC OBJECTIVE AIDS FOR

TROPICAL CYCLONE TWO (AL022009) 20090815 0000 UTC

...00 HRS... ...12 HRS... ...24 HRS. .. ...36 HRS...
090815 0000 090815 1200 090816 0000 090816 1200

LAT LON LAT LON LAT LON LAT LON
BAMS 14.5N 44.8W 14.9N 46.9W 15.9N 49.8W 17.5N 53.9W
BAMD 14.5N 44.8W 15.3N 47.1W 16.4N 49.8W 17.6N 53.0W
BAMM 14.5N 44.8W 15.0N 47.0W 15.9N 49.6W 16.8N 53.1W
LBAR 14.5N 44.8W 15.0N 47.5W 15.8N 50.5W 16.7N 54.0W
SHIP 25KTS 28KTS 32KTS 36KTS
DSHP 25KTS 28KTS 32KTS 36KTS

...48 HRS... ...72 HRS... ...96 HRS. .. ..120 HRS...
090817 0000 090818 0000 090819 0000 090820 0000

LAT LON LAT LON LAT LON LAT LON
BAMS 19.4N 58.2W 23.2N 66.9W 26.7N 73.0W 28.9N 75.6W
BAMD 18.8N 56.5W 21.0N 63.9W 23.5N 70.0W 24.9N 73.6W
BAMM 17.8N 56.9W 19.9N 65.1W 22.2N 72.5W 24.0N 77.7W
LBAR 17.7N 57.7W 20.2N 65.5W .0N .0W .0N .0W
SHIP 41KTS 50KTS 54KTS 59KTS
DSHP 41KTS 50KTS 54KTS 59KTS

...INITIAL CONDITIONS...
LATCUR = 14.5N LONCUR = 44.8W DIRCUR = 270DEG SPDCUR = 14KT
LATM12 = 14.6N LONM12 = 41.7W DIRM12 = 276DEG SPDM12 = 15KT
LATM24 = 14.3N LONM24 = 39.2W
WNDCUR = 25KT RMAXWD = 40NM WNDM12 = 25KT
CENPRS = 1007MB OUTPRS = 1010MB OUTRAD = 150NM SDEPTH = M
RD34NE = 0NM RD34SE = 0NM RD34SW = 0NM RD34NW = 0NM

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Quoting TampaSpin:
Looks like the GFS has TD2 becoming a very strong cane in front of 90L


GFS loses ex TD2. The cane is 90L with a new low behind it
Member Since: August 19, 2006 Posts: 0 Comments: 15816
3542. lennit
OOZ GFS should have recon info input into it..
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Quoting Weather456:
As soon as 90L reaches the islands, it shifts west under a building ridge


That building ridge just looks diurnal to me. Retreats beginning at sun set.
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3540. KEEPEROFTHEGATE (Mod)
AOI


(FORMER 02L)INV/91L


INV/90L
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Looks like the GFS has TD2 becoming a very strong cane in front of 90L
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Quoting Weather456:
As soon as 90L reaches the islands, it shifts west under a building ridge




456 i say we now have TD 3
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3537. Patrap
NEXRAD Radar
Miami, Echo Tops Range 124 NMI

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3536. 7544
Quoting Weather456:
As soon as 90L reaches the islands, it shifts west under a building ridge



looks a litlle further north this run correct
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Quoting stormsurge39:
Does anyone know if that is a surface low trying to form south of Cuba?


Thats an ULL spinning.......the surface low might be NE of that near the NE Cuban shore.
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90L is weaker on this run.. probably because it didn't develop yesterday (Friday).

Member Since: July 1, 2008 Posts: 13 Comments: 7387

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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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