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
Reader Comments
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Too much NHC bashing going on here. They did say it was more organized but the 48 hour forecast calls for a date with the shear monster.....
latest as of 301pm edt
I won! I won!
NHC fails, though.
Notice where the system is and where the dry air has shifted to?
Nar, it's a polar orbiting satellite thus becuz of its rotation, it overlaps between 40N and 40S. Thus the blank swaths.
Like I said I can see why they said what they said, it is based on the forecasted shear, those things can change
we will see how it plays out, but please lets cut the bashing
A 25 mph Invest isnt a threat to Birds..
Lighten Up Francis and Francine..
structure continues to improve though
You mean you want it to.
Floater 1 - AVN Color Infrared Loop
Convection strengthening in the band around it though. Not uncommon for early systems to have weaker central convection.
Floater 1 - Water Vapor Loop
AN OVERVIEW OF NHC PREDICTION MODELS
BAM - The Beta and Advection Model
The Beta and Advection Model is a baroclinic-dynamical track prediction model. It produces a forecast track by following a trajectory in the vertically averaged horizontal wind starting at the current storm location out to 120 hours. The trajectory is corrected to account for the variation of the Coriolis force with latitude, the so-called Beta effect. (Beta is the Greek letter frequently used in meteorological equations to represent the change in the Coriolis parameter with latitude.)
The figure shows how the conservation of absolute vorticity results in the formation of anticyclonic relative vorticity in the northeast quadrant of the storm, and the formation of cyclonic relative vorticity in the southwest quadrant of the storm: Diagram of absolute vorticity advection and relative vorticity formation in the vicinity of a tropical cyclone.. The result adds a component of motion to the northwest to the storm's trajectory.
Three versions of the BAM model are run with shallow (850-700 mb), medium (850-400 mb), and deep (850-200 mb) layers. All three versions of the model are run operationally four times per day.
Reference: Marks, D. G., 1992: The beta and advection model for hurricane track forecasting. NOAA Tech. Memo. NWS NMC- 70, 89 pp.
Low chance of development in the next 48 hours when you consider shear will increase tonight
Again if the shear forecast changes, than they will increase the chances for development.
Models Explained
What?
I do expect for 8PM tonight to have this system be declared as a medium (30% to 50%) by NHC... but by that time and due to the current organization that I'm seeing (upper outflow, good low inflow, and TSTM build up around the center) and if it keeps it up... I won't be surprised that it could be a TD before they even get into the High probability area.
20+ shear location will be critical for this system... but I believe it might be able to survive it as it has been attempting to stay shallow enough to keep itself on the southern end of the strong shear until conditions become a bit more favorable.
GFS is forecasting increased shear tonight and for the next few days, than favorable after that
shear not favorable by the GFS = low chance of development
Floater 1 - Water Vapor Loop
Lol
structure better organized however and DMIN is soon, so not too big of a deal
Viewing: 601 - 651
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