Tropical Weather Discussion
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AXNT20 KNHC 201031

Tropical Weather Discussion
NWS National Hurricane Center Miami FL
631 AM EDT Sat May 20 2017

Tropical Weather Discussion for North America, Central America
Gulf of Mexico, Caribbean Sea, northern sections of South
America, and Atlantic Ocean to the African coast from the
Equator to 32N. The following information is based on satellite
imagery, weather observations, radar and meteorological analysis.

Based on 0600 UTC surface analysis and satellite imagery through
1030 UTC.


A tropical wave is in the eastern Atlantic with axis extending
from 12N25W to 03N27W, moving west at 10-15 kt. The wave is
mainly in an unfavorable wind shear environment. Satellite imagery
also show Saharan dry air and dust in the wave environment, which
is supporting the lack of convection at the time.

A tropical wave is in the west Atlantic with axis extending from
14N56W to 05N56W, moving west at 20 kt within the last 24 hours.
CIRA LPW and SSMI TPW imagery show the wave is in a dry region. In
addition, unfavorable wind shear, Saharan dry air and dust are in
the wave environment supporting lack of convection at the time.

A tropical wave is in the far western Caribbean with axis
extending from 19N84W to 09N84W, moving west at 5-10 kt within
the last 24 hours. The wave continues embedded in a very moist
environment and is under a diffluent environment aloft that
support scattered heavy showers and tstms in the SW Caribbean S of
13N west of 80W.


The Monsoon Trough enters the tropical Atlantic near 08N13W and
continues to 07N23W. The ITCZ extends west of a tropical wave
from 06N29W to the coast of Brazil near 02N50W. Outside of the
convection associated with the tropical wave, no significant
convective activity is noted at this time.



Return flow prevails across the basin, which is advecting moisture
from the Caribbean into the NW Gulf to support dense fog N of 23N
west of 90W, according to both GOES IFR probabilities and surface
data. Showers in both the Bay of Campeche and the Florida Big
Bend coastal waters have dissipated. Water vapor imagery show dry
air across the remainder basin, which favors fair weather.
Otherwise, moderate southeasterly flow dominates basin-wide,
except for locally fresh winds off the Texas coast. No major
changes are expected until Sunday night when a weak cold front is
forecast to move off the Texas coast.


The tropical wave formerly over the far west Caribbean has moved
inland Central America. However, convection associated with the
wave continue to affect the SW basin where abundant moisture as
well as upper level diffluence support scattered heavy showers
and tstms. See the tropical waves section for further details.
Shallow moisture across the northern basin support cloudiness with
possible isolated showers today, but mainly dust has been
reported in the Dominican Republic as well as the Lesser Antilles.
The east Pacific monsoon trough extends from Panama to northern
Colombia and support scattered heavy showers and tstms S of 10N in
the SW Caribbean. Dry air subsidence from aloft and strong deep
layer wind shear support fair weather elsewhere. High pressure
over the Atlantic tightens the gradient in the Caribbean and leads
to strong to near gale force winds over the south-central
Caribbean, including the Gulf of Venezuela. Fresh to strong winds
are across the remainder of the central Caribbean, with fresh
southeasterly winds just north of Jamaica. Fresh to strong trades
will persist over the central Caribbean during the upcoming


Upper-level flow has become more zonal across the island with a
break in the heavy rainfall from the past few days. Moisture
is forecast to diminish over the upcoming weekend as the upper-
level trough continues to drift eastward and the wind flow turns
more to the NW. Fair weather is forecast during the day this
weekend, however model guidance suggest a high chance of showers
at night, both Saturday and Sunday.


Surface high pressure dominates the Atlantic Ocean being anchored
N of the area. The exception is a surface trough that extends
from 26N57W to 20N61W with scattered to isolated showers east of
the trough axis to 50W. See above for tropical waves information.

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