97L growing more organized, will bring heavy rain to the Lesser Antilles
The tropical wave near 12N 52W, about 600 miles east of the Lesser Antilles Islands (97 L), has grown more organized this morning as it tracks west at about 20 mph. This wave is surrounded by an area of very dry air from the Sahara Desert, but 97L has been able to steadily moisten a large region of the atmosphere over the past day, insulating itself from the dry air. This moistening process has been aided by sea surface temperatures (SSTs) that have steadily increased from 26.5°C to 27.5°C, plus the presence of only 10 knots of wind shear. The system now has a small area of intense thunderstorms near its center, with some rotation of the cloud pattern evident at mid-levels of the atmosphere. An upper-level outflow channel has opened to the north, and there is evidence that surface spiral bands are beginning to form. This morning's QuikSCAT pass missed 97L, so we don't know what is happening at the surface.
Wind shear is a modest 10 knots over the disturbance, and is forecast to remain in the moderate 10 - 15 knot range through Monday morning. This should allow further development to occur today, and 97L could be approaching tropical depression strength on Monday as it moves through the central Lesser Antilles Islands. Monday night, shear is expected to rise to 20 - 30 knots, thanks to the presence of a trough of low pressure at upper levels of the atmosphere over the eastern Caribbean. Since 97L is a relatively small system, it is very vulnerable to wind shear. This shear may be able to drive some of the dry air west of 97L deep into its interior, significantly disrupting the disturbance. Shear will remain high along 97L's path through Thursday, when the storm should be in the western Caribbean near Cuba. If there is anything left of 97L by then, some development is possible. The National Hurricane Center gave 97L a low (less than 30% chance) of developing into a tropical depression in the next 48 hours in their 8am Tropical Weather Outlook. However, I'd say the odds are now in the medium range (30 - 50%).
None of the computer models are forecasting tropical storm development over the next seven days.
Figure 1. Current satellite image of African wave 97L.
I'll have an update Monday morning. As 97L approaches the islands, you may want to follow local observations there using our wundermap for 97L.
Jeff Masters
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The increase in convergence is likely diurnal.
Probably, but last time we had none so it must be improving
Wind Direction (WDIR): ENE ( 70 deg true )
24-hour plot - Wind Speed Wind Speed (WSPD): 22.9 kts
24-hour plot - Wave Height Wave Height (WVHT): 7.9 ft
24-hour plot - Dominant Wave Period Dominant Wave Period (DPD): 8 sec
24-hour plot - Atmospheric Pressure Atmospheric Pressure (PRES): 29.88 in
24-hour plot - Pressure Tendency Pressure Tendency (PTDY): -0.04 in ( Falling )
24-hour plot - Air Temperature Air Temperature (ATMP): 80.8 F
24-hour plot - Water Temperature Water Temperature (WTMP): 81.1 F
24-hour plot - Dew Point Dew Point (DEWP): 75.7 F
24-hour plot - Heat Index Heat Index (HEAT): 86.7 F
That was a pretty big shower
http://www.meteo.psu.edu/~gadomski/COMPSHEARATL_0z/comploop.html
That wind/pressure chart sre shows that pressure tanking. Kinda hard to deny that.
Yeah, and so does that ship report
yep.
What is DMAX?
When cloud tops cool and convection explodes. Strongest just before suunrise
It's raining very heavily here now along with occasional gusty winds. Will get worse as the day goes on....
Tropical Cyclone Bulletin Number TWO
DEPRESSION BOB03-2009
11:30 AM IST July 20 2009
===================================
Subject: Depression over northwest Bay of Bengal
At 6:00 AM UTC, Depression BOB03-2009 over northwest Bay of Bengal remained practically stationary and lay centered near 21.0N 88.5E, about 120 km southeast of Digha, 160 km east-southeast of Balasore and 200 km southwest of Khepupara (Bangladesh).
The system is likely to intensify further and move in a west-northwesterly direction and cross north Orissa-West Bengal coast between Balasore and Digha today
That convection is induced by diurnal maximum and upper level diffluence. If it can make it through today, then we have something to watch.
convection is once again on the increase with 97L. this morning"s infra red pics are showing that 97L was able to fight off the high shear and retain it"s structure. water vapour loops show that the system is now at the base of the trough which is giving it some breathing space. last night 97L moved southwest for awhile but has resumed a west course shear is still 20 knots over the system and that will prevent much organisation. deveopment or not the system will bring heavy rains to barbados and the central windwards with gusts near storm force, most of today and a portion of tomorrow
Current conditions are cloudy with light winds ENE with periods of heavy rain.
Info taken from Station 41101
Wind Direction (WDIR): E ( 80 deg true )
Wind Speed (WSPD): 22.9 kts
Wave Height (WVHT): 6.6 ft
Dominant Wave Period (DPD): 7 sec
Atmospheric Pressure (PRES): 29.90 in
Pressure Tendency (PTDY): +0.02 in ( Rising )
Air Temperature (ATMP): 81.3 °F
Water Temperature (WTMP): 81.5 °F
Dew Point (DEWP): 75.6 °F
Heat Index (HEAT): 87.8 °F
Combined plot of Wind Speed, Gust, and Air Pressure
Quiet.
rgr that.
eastern carrib is the dead zone...
Tropical Invest 97L heads for the Windward Islands
After more rambling about shear in a day the end result is that 97L is still there effected by shear but there.
No closed surface low but unflagged tropical storm force winds! Plus it appears to be getting better organised on satellite pictures.
Morning guys
Good update W456, Have to say I follow your post closely.
Now one interesting thing to note is that the time and location of this meeting point should prove interesting... since in my point of view 97L is in the eastern side of the trough which at this time is the worst part and later today it should a not so head on position with the shear... so should be interesting to see if the DMAX/Diffluence induced convection can stick around while it enters the E/C Carib. Of course not saying conditions are favorable in the CARIB as there's still shear left in there...
Also just in case... I've combined the latest 850MB through 500MB level VORT MAX charts and you can see the mid level shear has been displaced from the low shear VORT MAX due to shear.
Viewing: 2151 - 2201
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