Disturbance 90L close to tropical depression strength; TD 2 may rise again
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
Reader Comments
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TCDAT3
TROPICAL DEPRESSION THREE DISCUSSION NUMBER 1
NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL AL032009
1100 AM AST SAT AUG 15 2009
SATELLITE IMAGERY AND QUIKSCAT DATA INDICATE THAT THE BROAD AREA OF
LOW PRESSURE OVER THE EASTERN ATLANTIC HAS FORMED A WELL-DEFINED
CIRCULATION AND SUFFICIENTLY ORGANIZED CONVECTION TO BE DESIGNATED A
TROPICAL DEPRESSION. THE INITIAL INTENSITY IS 30 KT BASED ON THE
QUIKSCAT DATA...AS WELL AS SATELLITE INTENSITY ESTIMATES OF 30 AND
35 KT FROM SAB AND TAFB.
THE SYSTEM IS CONSOLIDATING SOUTH OF WHERE THE CENTER WAS BEING
TRACKED YESTERDAY...AND THE INITIAL MOTION IS A SOMEWHAT UNCERTAIN
265/15. SOME ERRATIC MOTION IS POSSIBLE TODAY AS THE DEPRESSION
INTERACTS WITH THE ELONGATED MONSOON/TROPICAL WAVE CIRCULATION THAT
SPAWNED IT. OVERALL...DEEP-LAYER HIGH PRESSURE OVER THE CENTRAL
AND EASTERN ATLANTIC SHOULD STEER THE CYCLONE GENERALLY WESTWARD
FOR THE NEXT COUPLE OF DAYS...FOLLOWED BY A TURN TOWARD THE WEST-
NORTHWEST. THE TRACK MODEL GUIDANCE IS IN GOOD AGREEMENT WITH
THIS SCENARIO...AND THERE IS A FAIRLY TIGHT CLUSTER OF THE MODELS
AROUND THE 5 DAY FORECAST POINT. ONE EXCEPTION IS THE ECMWF...
WHICH FORECASTS SIGNIFICANTLY MORE NORTHWARD MOTION THAN THE OTHER
MODELS AND AT THIS TIME IS A RIGHT OUTLIER.
THE CYCLONE IS IN DEEP-LAYER EASTERLY FLOW WITH LIGHT/MODERATE
VERTICAL WIND SHEAR FORECAST FOR AT LEAST THE NEXT 4 DAYS. ALL
INTENSITY GUIDANCE FORECASTS THE SYSTEM TO BECOME A HURRICANE BY
THE END OF THE FORECAST PERIOD...WITH THE HWRF FORECASTING A MAJOR
HURRICANE. THE INTENSITY FORECAST THUS CALLS FOR GRADUAL
STRENGTHENING TO A TROPICAL STORM IN 12 HR AND A HURRICANE IN 72-96
HR IN BEST AGREEMENT WITH THE INTENSITY CONSENSUS MODELS.
FORECAST POSITIONS AND MAX WINDS
INITIAL 15/1500Z 11.5N 34.0W 30 KT
12HR VT 16/0000Z 11.3N 36.1W 35 KT
24HR VT 16/1200Z 11.3N 38.9W 40 KT
36HR VT 17/0000Z 11.8N 41.7W 45 KT
48HR VT 17/1200Z 12.4N 44.4W 50 KT
72HR VT 18/1200Z 14.0N 50.5W 60 KT
96HR VT 19/1200Z 16.5N 57.0W 75 KT
120HR VT 20/1200Z 19.0N 63.0W 90 KT
$$
FORECASTER BEVEN
"Ana is dying" is misinformation.
Also in 2007 for TD4's first advisory.
72HR VT 16/1200Z 13.0N 51.0W 60 KT
96HR VT 17/1200Z 14.5N 57.5W 75 KT
120HR VT 18/1200Z 16.0N 63.5W 90 KT
Astonishing.
I'm not riping anything, I was talking about the dead on forecast track of ana right over me.
...ANA...PRONOUNCED AH-NA...MOVING QUICKLY WESTWARD WITH LITTLE
CHANGE IN STRENGTH...
About Destin for the 0 Z.
I completely agree.
i got your back 456
i edited my post, dead on track, not dead one
A track that close to Hispaniola could have severe consequences on the circulation.
StormW doesn't post on weekends.
The good thing is that there's about a week to prepare for these two storms.
Woops, scratch my last post then I thought you were talking about land interaction.
nothing changes here
At the end of his last post it stated he will have an update Saturday morning
Weather, you better watch out for these. We don't wanna lose you. Who else will post accurate data other than Dr. Masters?
I should have rephrased that. Any slight deviation might work in our favor. We should be keeping an eye on both these systems.
Not looking good for the N. Leewards next week. Getting hit with 3 different systems in a row.
Link
For a storm that just formed it is.
you're safer in Pentasookee, Utah
watch for snow-ins tho - and the occasional bear / mormon
GFS develops the African wave in the Sunday-Monday range, something else to watch behind our two current systems. The environment is still pretty favorable in that area.
Viewing: 5201 - 5251
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