Tropical Weather Discussion
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AXNT20 KNHC 210604

Tropical Weather Discussion
NWS National Hurricane Center Miami FL
204 AM EDT Sun May 21 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 0000 UTC surface analysis and satellite imagery through
0545 UTC.


A tropical wave is in the central Atlantic with axis extending
from 11N28W to 02N30W, moving west at 10 kt within the last 24
hours. The wave is in a region of unfavorable wind shear and
most of the wave environment is under the Saharan dry air and
dust, which is hindering convection.

A tropical wave is in the far eastern Caribbean with axis
extending from 15N61W to inland Venezuela near 07N61W, moving
west at 15 kt within the last 24 hours. Similar to the wave in the
central Atlantic, the wave environment is characterized by
unfavorable wind shear, and the presence of abundant Saharan dry
air and dust, which support the lack of convection.


The Monsoon Trough enters the tropical Atlantic near 09N13W and
continues to 07N20W. The ITCZ extends from 07N20W and then
continues to 06N29W, then resumes west of a tropical wave at
06N31W to the coast of Brazil near 02N50W. Scattered moderate
convection and tstms are from 04N-09N east of 20W.



Numerous heavy showers and tstms are over Alabama and within 90 nm
off the coast extending SW to Louisiana and Mississippi coastal
waters. Moisture advection from the Caribbean by SE wind flow and
upper level diffluence between a ridge over the eastern CONUS and
a trough over the central plains support this convection. Strong
winds up to 30 kt are associated with this area of convection off
the coast. Another region of upper level diffluence is between the
base of the trough over Texas and westerly flow across the Gulf.
This upper level environment supports scattered moderate
convection within 120 nm off the coast of Texas ahead of the next
front to enter the basin Monday night. Moderate return flow
dominates the basin, except within 135 nm off the northern
Yucatan Peninsula where a surface thermal trough support fresh
winds. A second and stronger cold front is forecast to come off
the Texas coast Tuesday night.


Numerous heavy showers and tstms are in the SW Caribbean S of 12N
associated with the monsoon trough that crosses Costa Rica and
Panama to a low over NW Colombia as well as upper level
divergence. The pressure gradient between strong high pressure in
the Atlantic and lower pressure across the western half of the
basin continue to support fresh to strong winds with the strongest
winds being within 150 nm off the Colombia coast and in the Gulf
of Honduras. Latest scatterometer data indicate fresh NE flow
across the Windward Passage. Moderate trades and shallow clouds
with possible isolated showers are across the remainder basin.
Otherwise, a tropical wave lacking convection has entered the far
eastern Caribbean. For further details see the tropical waves


Daytime heating, local sea breezes and mountain upslope lifting
will combine with available shallow moisture to produce some
cloudiness with scattered to isolated showers mainly during the
afternoon and early evening hours Sunday and Monday.


High pressure prevails across most of the Atlantic Ocean being
anchored by a 1023 mb high east of Bermuda and a 1024 mb high in
the central basin near 28N38W. A middle to upper level trough
between 55W and 70W continue to support s surface trough NE of the
Virgin Islands from 23N59W to 17N62W. Scattered to isolated
showers are mainly east of the trough N of 19N between 50W and
60W. A cold front will enter the north central Atlc waters Monday
night. Otherwise, surface high pressure will dominate elsewhere.

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