A tropical wave
(Invest 94L)
that moved off the coast of Africa on Saturday was located near 12°N,
26°W on Monday morning, and could potentially be a tropical storm when
it arrives in the Lesser Antilles Islands on Saturday.
Satellite loops show the wave has a modest amount of spin and respectable amount of heavy thunderstorms.
Water vapor satellite images and the
Saharan Air Layer analysis
show that 94L is located in a fairly moist environment, with the dry
air coming off or Africa located well to the north and west of the
disturbance.
Wind shear was a high 25 knots, but the
8 am EDT Monday run of the SHIPS model
predicted that wind shear would fall to the low range, 5 - 10 knots, by
Wednesday. Sea Surface Temperatures beneath 94L were 27°C on Monday,
but were predicted to fall to 25.5°C by Wednesday, limiting the
potential for development through Wednesday. The wave is headed west at
15 - 20 mph, and by Friday, will move over warmer waters of 27°C, as the
storm nears the Lesser Antilles Islands. However, 94L will gain some
latitude as it approaches the islands, and move into increasingly dry
air to the northwest. These conditions are similar to what Bertha
encountered as it approached the islands. If 94L does develop, the odds
are that it will be a storm similar to Bertha--struggling against dry
air, never reaching hurricane strength in the islands. Arrival in the
islands should occur on Saturday, according to the Monday morning runs
of the GFS and European models. None of the reliable computer models for
predicting tropical storm formation (GFS, European, and UKMET) develop
94L, but about 1/3 of the 20 members of the GFS model ensemble show
development late this week (the GFS ensemble is a set of 20 runs of the
GFS model done at lower resolution with slightly different initial
conditions to generate an uncertainty "plume" of model runs.) None of
these ensemble forecasts showed 94L reaching hurricane strength. In
their 8 am EDT Monday Tropical Weather Outlook, NHC gave 94L 2-day and
5-day development odds of 0% and 30%, respectively.
Figure 1.
Satellite analysis of the Saharan Air Layer (SAL) done at 8 am EDT
August 11, 2014, showing Invest 94L lying just south of a large area of
dry air that covered much of the Atlantic. Image credit:
University of Wisconsin CIMSS/NOAA Hurricane Research Division.Jeff Masters
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