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AXNT20 KNHC 211910 AAA

Tropical Weather Discussion...Updated
NWS National Hurricane Center Miami FL
210 PM EST Tue Feb 21 2017

Updated to include new conevction under ITCZ/Monsoon Trough

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
1830 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 details.

...ITCZ/MONSOON TROUGH... 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.

An increasing area of scattered moderate/isolated strong
convection is noted from 01N to 06N west of 45W to the coast of
South America.


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 the 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
Finally...the remainder of the eastern Atlc is under the
influence of another surface ridge anchored by a 1031 mb high
centered to the northeats of the Azores near 44W19W. The ridge
axis extends southwestward from the high to 32N31N to 17N43W.

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