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Posted: Fri Aug 22nd, 2008 10:59 pm |
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Disturbance 94L approaching the Lesser Antilles
Heavy thunderstorms associated with a tropical wave (94L) near 11N, 54W, about 500 miles east of the Lesser Antilles Islands, have grown more concentrated in recent hours. This disturbance could be trouble, and bears careful scrutiny. This morning's QuikSCAT pass mostly missed 94L, but did show a pronounced wind shift at the western edge of the disturbance. Visible satellite loops show some evidence of rotation and increase in heavy thunderstorms, but I'm also seeing surface outflow boundaries to the southeast, indicating that dry is getting sucked into the thunderstorms and creating downdrafts that rob the disturbance of energy. Wind shear has fallen to a modest 10 knots over 94L, and the dry air surrounding it has been steadily moistening. Wind shear is expected to drop to a low 5 knots and remain low for the next four days, and NHC is giving this system a medium (20%-50% chance) of developing into a tropical depression by Sunday afternoon. I would put the odds at 40%-70%. Three of our reliable computer models develop the storm. It's easy to see why--the wind shear forecast for the Caribbean calls for very low values of wind shear below 5 knots for most of the coming week (Figure 2). The GFDL calls for 94L to develop into a Category 2 hurricane that threatens Jamaica on Tuesday. The HWRF doesn't develop 94L at all, and the ECMWF and NOGAPS models call for 94L to eventually develop late next week after it moves north of Hispaniola, into the Bahama Islands. All of these models used the wrong starting position of 94L, since the storm re-formed 150 miles to the east of where the models were expecting it to be. Thus, we can put little faith in the details of forecast track of 94L predicted by the models. A track through the Caribbean towards Jamaica currently appears to be the highest probability track to me. Residents of the Lesser Antilles can expect heavy rain and 40 mph wind gusts from 94L when it blows through Saturday and Sunday. Residents of the Dominican Republic, Haiti, and Jamaica should keep a careful eye on this potentially dangerous disturbance.
Figure 2. Wind shear forecast for the Atlantic for 2 am EDT Monday August 25 2008, as predicted by this morning's 2 am EDT run of the GFS model. Very low values of winds shear (red colors) are predicted for the entire Caribbean and Gulf of Mexico. Winds shear values less than 8 m/s (approximately 16 knots, the three red colors) are conducive for tropical storm formation.
Disturbance 95L in the middle Atlantic
Another tropical wave (95L), near 19N 41W, halfway between Africa and the Lesser Antilles Islands, remains disorganized. This morning's QuikSCAT pass showed only a slight wind shift associated with 95L , and no closed circulation. Top winds were about 30 mph. Wind shear is a modest 10 knots over 95L, and is forecast to remain near 10 knots for the next five days. Visible satellite loops show only a small clump of heavy thunderstorm activity, and NHC has downgraded 95L's chance of developing into a tropical depression in the next two days to low (<20% chance).
My next blog will be Saturday.
Jeff Masters
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Posted: Fri Aug 22nd, 2008 11:01 pm |
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[/code]For the North Atlantic...Caribbean Sea and the Gulf of Mexico...
[code]The National Hurricane Center is issuing advisories on Tropical
Storm Fay...located inland about 40 miles north-northeast of Cedar
Key Florida.
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A large but disorganized area of disturbed weather centered about
350 miles east of the Windward Islands is moving to the west-
northwest at 15 mph. Any development of this system should be slow
to occur during the next couple of days. Regardless of
development...locally heavy rains and gusty winds are expected to
overspread portions of the leeward and windward tonight and
continue into tomorrow.
A tropical wave located about 1300 miles east of the Leeward Islands
is producing some disorganized showers and thunderstorms.
Development...if any...of this system should be slow to occur over
the next couple of days as the wave moves toward the west or
west-northwest at about 20 to 25 mph.
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Elsewhere...tropical cyclone formation is not expected during the
next 48 hours.
Attachment: Picture 3.png (Downloaded 21 times)
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Posted: Sat Aug 23rd, 2008 03:00 pm |
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The forecast for 94L
The GFDL model, which with yesterday's run was developing 94L into a powerful hurricane that threatens Jamaica, is no longer developing the storm. The ECMWF, NOGAPS, and Canadian model all develop 94L. They foresee the system will enter the eastern Caribbean Sunday, jog northwest and affect the Dominican Republic on Tuesday, then develop into a tropical depression by Thursday near the Dominican Republic or eastern Bahama Islands. The wind shear forecast for the Caribbean calls for very low values of wind shear below 5 knots for most of the coming week (Figure 2). Residents of the Lesser Antilles can expect heavy rain and 40 mph wind gusts from 94L when it blows through Saturday night through Sunday. Residents of the Dominican Republic, Haiti, and Jamaica should keep a careful eye on this potentially dangerous disturbance.
Figure 2. Wind shear forecast for the Atlantic for 2 am EDT Monday August 25 2008, as predicted by this morning's 2 am EDT run of the GFS model. Very low values of winds shear (red colors) are predicted for the entire Caribbean and Gulf of Mexico. Winds shear values less than 8 m/s (approximately 16 knots, the three red colors) are conducive for troical storm formation.
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Posted: Sat Aug 23rd, 2008 03:02 pm |
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I'm guessing 94 will stay south of Culebra.....but there may very well be some outer bands of rain and wind......
Attachment: Picture 5.png (Downloaded 13 times)
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