Science Tropical Weather

Invest 93L / Pouch P09L

A tropical wave that came off the coast of Africa a few days near the Cape Verde Islands was designated as 93L by the NHCinfoNHCNational Hurricane Center yesterday afternoon. With the exception of Hurricane Arthur, this is the first significant wave with a “possibility” of development. Previous waves were pretty much not given a chance to develop due to SALinfoSALSaharan Air Layer and upper level winds.

During the early morning hours, 93L is somewhat disorganized but has been a slowly progressing in getting some deep convection which is extremely vital for tropical cyclone development. If fact during the day today, 93L has much better organized since earlier this morning. 93L is far enough south of the SAL and at least for the time being, is not a factor although 93L is still attached to the ITCZinfoITCZIntertropical Convergence Zone - Area encircling the earth near the equator where the northeast and southeast trade winds come together.. Both the two major models, the GFS and the ECMWF model camps are forecasting to build an anti-cyclone over over 93L as it tracks westward toward the Lesser Antilles. This should allow relaxation of the upper level winds and possibly let further consolidation of the entire system.

Satellite photo of Invest 93L

Credit: American Weather Model Center

GFS Model
GFS Model 1800z at 135 hours

Credit: American Weather Model Center

ECMWF Model 1800z at 120 hours

Credit: American Weather Model Center

The GFS and the ECMWF seem to want to 93L to develop into at least a tropical depression some time later in the week, the ECMWF is a bit faster than the GFS and even the UKMET. Currently, 93L is tracking westward (with a slight north of west) and this movement should continue for the next 3-4 days. Although the global models may feel there is weakness in the ridge along with a trof over the east coast of the US, this should enough to allow 93L to turn WNW then NW before entering the area just east of the Northern Leeward Islands. The ECMWF though is faster and goes through the islands before turning NW. Guidance at this point in time would be sheer speculation. If factors such as shear, SAL, etc. occur, then those factors could alter the steering currents. Although this seems unlikely, anything is possible in the tropics.

All those in the Great Antilles to the Leeward Islands need to monitor 93L closely for any significant changes in both the track and the possibility of early development of a tropical cyclone.

Remember, always stick with official information such as your local WFO and the NHC.