Tropical Weather Discussion
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AXNT20 KNHC 211805

Tropical Weather Discussion
NWS National Hurricane Center Miami FL
105 PM EST Tue Feb 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 1200 UTC surface analysis and satellite imagery through
1745 UTC.

A 1010 mb surface low associated with an anomalously south deep
layer low is near 24N63W. A cold front extends from the low
southwestward to the northeast portion of the Caribbean Sea. These
features are within a broad area of low pressure over the central
Atlantic present north of 19N between 50W and 71W. A second cold
front enters the area through 32N59W, and continues to 27N70W.
This cold front will merge with the cold front that extends from
the low by this evening as the low continues moving southeastward
while weakening. The merged cold front is forecast to be along a
position from near 32N53W to 16N61W this evening. A very tight
pressure gradient will become established between the front and
strong high pressure to its east. This will induce near gale to
gale force south to southwest north of 27N within 240 nm east of
the merged front. The gale force winds are expected to lift north
of the discussion by Wednesday night. See latest NWS High Seas
Forecast under AWIPS/WMO headers MIAHSFAT2/FZNT02 KNHC for more

The Monsoon Trough extends from the African coast near 08N13W to
04N18W. The Intertropical Convergence Zone axis extends from
04N18W to the Equator near 27W and along the Equator to 38W.
Scattered moderate convection is within 60 nm of the axis between
14W and 18W. Scattered moderate is observed north of the ITCZ
within 60 nm of a line from 03N30W to 03N36W.


Water vapor imagery shows a deep layer low centered over southern
Arkansas extending into northern Louisiana. A deep layer trough
extends from the low over the central Gulf waters and to the
eastern Bay of Campeche. The troughing supports a 1008 mb low
centered over northwest Mississippi, with a cold front dropping
south-southwest from the low to 30N88W to 25N91W to just southeast
of Veracruz Mexico. A post-frontal trough enters the northwest
portion from near Galveston to near 27N95W. A squall line is just
ahead of the cold front north of 27N. Scattered thunderstorms,
increasing with time, are along and within 60 nm east of the
squall line. Scattered showers and isolated tstms are seen
elsewhere along and east of the cold front north of 27N. Strong
middle to upper level diffluence occurring east of the deep layer
trough is helping to enhance this activity. Scattered showers are
elsewhere along and within 60 nm east of the front, and within
120 nm northwest of the front.

Otherwise...the eastern half of the basin is under the influence
of surface ridging that stretches from the NE United States
southwestward to that portion of the basin. Latest satellite
imagery is showing extensive middle to upper level cloudiness
streaming eastward ahead of the aforementioned deep layer tough
and cold front to across just about the entire Florida peninsula.
Mostly clear skies are behind the cold front where water vapor
imagery shows very dry conditions under strong strong subsidence
present there. The exception is in the northwest portion of the
Gulf where scattered showers and thunderstorms have developed
within 60 nm east of the post-frontal trough.

Looking ahead...the cold front is forecast to move into the
eastern Gulf by tonight as the post-frontal trough merges with
it. The merged front is forecast to reach a position from the
eastern section of Florida panhandle to the Yucatan Channel
tonight as a surface low forms along the front near 28N85W. The
low will move southeastward on Wednesday, and move across the
Florida peninsula near 27N pushing the front through the Straits
of Florida late on Friday. Strong northwest winds behind the front
will diminish to moderate northeast through Thursday as high
pressure in the wake of the front weakens.

Overall the Caribbean basin continue under fairly tranquil
conditions this afternoon, with the exception of the northeastern
waters. There an area of low pressure N-NE of Puerto Rico
centered near 24N63W extends a cold front rather far to the
southwest to just south of Antigua, to over Montserrat and to near
16N71W. Low level moisture convergence within southerly winds
focused along a surface trough analyzed from Saint Martin south-
southwest to near 12N65W is generating widely scattered showers
and isolated thunderstorms north of 15N east of the trough. This
activity will gradually shift east of the basin through tonight
as the trough is forced eastward in response to the cold front
pushing south-Southeast. Otherwise...dry and stable air aloft
coupled with gentle to moderate east to northeast winds are
prevailing and expected to persist through tonight, except in the
northwest portion of where a cold front currently moving through
central Gulf of Mexico will make its entrance. The cold front will
reach from central Cuba to he northeast side of Nicaragua
Wednesday night, then become stationary from eastern Cuba to
northeast Nicaragua late on Thursday. Strong northwest flow will
briefly follow in behind the front on Wednesday before diminishing
to fresh west to northwest winds on Thursday.

Scattered to locally broken low clouds with possible developing
isolated showers are observed along and just inland much of the
northern coast of the island, and over much of the northwest
corner of Haiti. Patches of low-level moisture moving southward
due to northerly flow to the west of the Atlantic low pressure
system and cold front will approach the north coast of the island
today and tonight providing for chances of precipitation. Any
shower activity that approaches the north coast will be moving
rather quickly to the south.

A broad area of low pressure is noted across the SW North Atlc
focused on a 1010 mb low centered near 24N63W. The associated
cold front extends southwestward to the northern Caribbean Sea.
Abundant deep layer moisture is evident to the east of the low and
cold front as it is being supported by a very pronounced sharp
deep layer trough that enters the area through 32N60W, and
continues southward to the deep layer low at  middle/upper level
low at 21N60W. The instability present east of the trough in
conjunction with the deep layer moisture is producing scattered
showers and thunderstorms north of 17N between 50W and 61W. The
low and its associated cold front is forecast to continue moving
eastward and merge with another cold front that extends from
32N59W to 27N70W as of 12Z. The entire system will move further
eastward over the central Atlantic by Wednesday producing the
Special Features near gale to gale force conditions mentioned
above. New low pressure will move from the Gulf of Mexico
northeastward to near 27N80W by Thursday morning, with a trailing
cold front. Strong to near gale east-southeast winds are expected
east of the low to near 71W.

Otherwise...the remainder of the SW North Atlc is under the
influence of a surface ridge anchored by a 1032 mb high centered
over New England. The ridge will slide offshore through Wednesday.
Finally...the remainder of the eastern Atlc is under the
influence of another surface ridge anchored by a 1031 mb high
centered NE of the Azores near 44W19W. The ridge axis extends
southwestward from the high to 32N31N to 17N43W.

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