Tropical Weather Discussion
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AXNT20 KNHC 181805

Tropical Weather Discussion
NWS National Hurricane Center Miami FL
205 PM EDT Tue Apr 18 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.


The Monsoon Trough axis extends across the western Africa coast
near 07N11W and continues to 04N37W to 01N22W. The Intertropical
Convergence Zone continues from 01N22W to 00N39W. Scattered
moderate/isolated strong convection is within 60 nm north
of the axis between 14W-17W, and within 60 nm south of the
axis between 17W-21W. Scattered moderate convection is within
60 nm north of the axis between 21W-29W and within 30 nm of
the axis between 32W-39W.



A 1024 mb high is centered over the western Atlantic near 29N67W
with a surface ridge extending across northern Florida to the
northern Gulf of Mexico along 29N. A surface trough, identified
very well in the surface isobaric pattern and in satellite
imagery, extends from near 29N83W to 23N85W. The combination of
this trough and a shortwave trough swinging eastward over the
eastern Gulf is resulting in ample deep atmospheric moisture and
instability over that portion of the Gulf. Both satellite and
radar imagery shows scattered to numerous showers and
thunderstorms from 24N to 26N east of 85W to just west of the
Florida Keys and southwest Florida. This activity is capable of
producing strong gusty winds as it shifts generally towards the
northwest. Gentle to moderate east to southeast flow is noted
elsewhere across the basin. A rather vigorous mid to upper level
trough is observed on water vapor imagery to be moving through
eastern Texas. A surface trough is along and just inland the Texas
coast. Very deep moisture ahead of the troughs and divergence
aloft is supporting a an almost solid line of scattered moderate
to isolated strong convection over the far northwest waters north
of 26N between 94W and just inland the Texas coast north of
Galveston. Weakening scattered moderate convection is to the south
within 30 nm either side of line from 26N95W to 24N96W to
21N96.5W. This activity is expected to continue on weakening
through this afternoon and evening as drier air is advected in
behind it. The surface high pressure ridge is forecast to weaken
some on Wednesday.


Upper level disturbances ridging along in strong southwest to
west flow associated with a jet stream branch that rounds the
base of a sharp mid/upper level trough over eastern Texas are
combining with ample moisture and instability along with low level
moist easterly flow resulting in an increasing area of scattered
moderate/isolated strong convection from 16N to 21N between 80W
and the coast to Belize and the Yucatan Peninsula. Scattered
showers and isolated thunderstorms are seen elsewhere west of 78W.
This activity will continue to increase and expand in coverage
through afternoon and evening, and gradually shift eastward
through Thursday as the tough axis migrates eastward to the
eastern Gulf of Mexico. Another upper level disturbance aloft
riding eastward in westerly flow has enhanced scattered shower
and thunderstorm activity over the northern eastern Caribbean
Sea within 30 nm of line from 16N69W to 17N66W. Isolated showers
and thunderstorms are observed elsewhere east of 71W. The
upper atmospheric pattern with disturbances riding in the
westerly flow in combination with plenty of moisture and
instability favors the eastern Caribbean and majority of
Lesser Antilles and also Puerto to be quite active with scattered
to possibly numerous at times showers and thunderstorms through
Friday. Northeast winds will increase to strong category at night
near and through the Windward Passage Wednesday and Thursday.


High level clouds are seen streaming eastward over Hispaniola,
however, for the most part they are rather thin allowing for
daytime heating to filter through these clouds. This in
combination with plenty of atmospheric instability is allowing for
isolated showers and thunderstorms to develop over the interior
of the island, and over the southwest section of Haiti. Similar
activity is over the nearby waters. The trend appears for
additional moisture and instability to exist over and near
Hispaniola through Friday. This is expected to set off additional
shower and thunderstorm activity, especially if there are breaks
in the presently observed upper clouds to allow for more heating
would help provide further impetus for the development of
additional activity. Some of the shower and thunderstorm may bring
locally heavy rainfall to some locations.


A 1024 mb high is centered over the western Atlantic near 29N67W.
To the east, a deep low of 994 mb is centered at 32N44W with
strong to near gale force winds to its north and south to near
27N between 41W and 52W with seas of 13 to 17 ft. A trough,
formerly a cold front, is to its east from near 32N36W to 23N34W
to 18N44W. Another surface trough extends from the low 29N45W and
northwest to 30N48W. Scattered showers and thunderstorms are
noted north of 27N between 39W and 46W. The low is forecast to
move east during the next 24 hours, reaching near 32N42W with
pressure of 998 mb and associated strong to near gale force
winds north of 31N between 35W and 40W. By Thursday, the low
is forecast to track to north of the area near 34N39W with
a pressure of 995 mb, with gale force winds over its northeast
semicircle. Scattered showers and isolated thunderstorms south
of 27N and west of 70W will change little through Thursday as
mid/upper level troughing stays west of the basin with
upper level disturbances moving eastward ahead of it to the
area of the Bahamas and to near 70W. The 1024 mb high is
forecast to dissipate Wednesday. Little change is expected

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