AXNT20 KNHC 250605
Tropical Weather Discussion
NWS National Hurricane Center Miami FL
205 AM EDT Tue Jul 25 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
A far eastern Atlantic tropical wave has its axis along 19W from
16N to 06N, moving westward at 10-15 kt. This wave remains
embedded within a very moist southwesterly wind flow regime
associated with the monsoon trough that has becomes well
established off the coast of Africa. Model guidance from the GFS
indicates that broad 700 mb troughing exists over the area where
the wave is located. Latest satellite imagery along with the Total
Precipitable Water (TPW) imagery depict an increasing deep
atmospheric moisture layer enveloping the wave. Scattered moderate
isolated strong convection is increasing east of the wave within
30 nm of a line from 13.5N19W to the coast of Africa at 14N17W.
Scattered moderate convection is within 30 nm either side of a
line from 10N19W to 10N15W. Scattered showers and isolated
thunderstorms are elsewhere east of the wave, and within 120 nm
west of the wave from 10N-16N.
A tropical wave has its axis extending from 15N30W to 09N31W
to 03N31W, moving westward around 15 kt. This wave remains
suppressed, convectively and structurally speaking, as it moves
through a region of the Atlantic where a very stable environment
is present, with the added factor of Saharan dry air and related
dust as clearly seen on satellite imagery. The only portion of the
wave that remains moist and unstable is that to the south of 09N
and across the monsoon trough. Scattered moderate convection is
within 180 nm either side of the wave from 06N-08N.
A broad central Atlantic tropical wave has its axis extending
from near 23N45W to 16N43W to 09N43W, moving westward at 10-15
kt. The wave lies under the eastern edge of 700 mb troughing. The
wave remains obsolete of deep moisture, with the exception of the
portion from 17N-23N between 44W-47W as seen in TPW imagery.
Latest satellite imagery shows scattered showers and isolated
thunderstorms within this area of moisture. An upper level low
just west of the wave at 24N49W is moving westward in tandem with
the wave, and it is assisting with development of the shower and
A tropical wave is approaching the Lesser Antilles, with its axis
extending from near 18N55W to 11N56W to the coast of South America
at 06N56W. It is moving westward at 10-15 kt. Broad 700 mb
troughing is indicated by the models to be present over the
northern and central portions of the wave, however, the presence
of dry air aloft as noted in water vapor imagery is only allowing
for isolated showers and weak isolated thunderstorms near those
portions of the wave. A diffluent flow aloft provided by an upper
trough that exists across the northern part of the wave, and
ridging across the southern part of the wave is helping to
support increasing scattered shower and thunderstorm activity
within an area from 11N-14N between 53W-61W. The wave will cross
the Lesser Antilles tonight, and move across the eastern Caribbean
on Wednesday. Moisture associated with this wave is forecast
to bring increasing chances for scattered showers and
thunderstorms to the the eastern Caribbean on Wednesday, however,
before the wave arrives there scattered showers and thunderstorms
ahead of it will move across portions of mainly the Leeward
Islands today. Some of this activity may be attendant by gusty
The monsoon trough axis extends from 12N16W to 08N27W to 07N37W,
where scatterometer data indicates the ITCZ begins and continues
to 06N42W to 07N46W to 10N53W. Besides the convection mentioned
described above in relation to analyzed tropical waves, scattered
moderate convection exists within 120 nm north of the axis
between 33W-35W, within 90 nm south of the trough between 20W-26W,
and north of the ITCZ within 30 nm of 10N49W.
GULF OF MEXICO...
In the upper levels, an upper level low is centered near 25N93W.
A cyclonic shear axis extends from the low east to 25N84W, and
southwest from the low to 22N98W. Deep moisture has increased
across just about the entire Gulf during the past 24 hours. The
earlier scattered moderate to isolated strong convection that was
over the Yucatan Peninsula and Cuba is quickly dissipating.
Scattered showers and isolated thunderstorms over some areas
of the SW Gulf, and far south-central Gulf. Isolated showers
are elsewhere. At the surface, a 1019 mb high is near 27N84W.
The related anticyclonic flow consists of gentle to light
and variable winds E of 91W and moderate easterly to southeasterly
flow over the W Gulf. Little overall change is forecast in the
current synoptic set-up through the next couple of days.
Scattered moderate to isolated strong convection is again expected
to develop over the the Yucatan Peninsula and Cuba this afternoon
and last into this evening.
Just about the entire the Caribbean is under moderate subsidence
aloft and dry sinking air, with the exception of the southern
portion of the eastern Caribbean where scattered showers and
isolated thunderstorms moving quickly westward are seen. Similar
activity is over the northwest portion of the sea. In the far SW
part of the sea, the eastern extension of the eastern Pacific
monsoon trough along with low-level speed convergence is
supporting isolated showers and thunderstorms along and just
inland the coast of northern Panama. The pressure gradient across
the area will maintain fresh to strong winds across the central
Caribbean through tonight, except for near gale force winds along
the NW coast of Colombia tonight. The pressure gradient will then
relax on Wednesday, with strong nocturnal trades expected mainly
along the coast of Colombia. Moderate to locally fresh trades will
prevail elsewhere across the Caribbean at that time. A tropical
wave will move across the eastern Caribbean on Wednesday. See
above for a discussion on this feature.
Scattered showers and thunderstorms that were over most of Haiti
last night have dissipated. Isolated showers are possible over
the waters just west of Haiti. Dry air aloft continues to advect
west across much of the island. This should keep deep convection
to a minimum over the island this afternoon and evening, and
again on Wednesday. Some moisture may approach the eastern
part of the island late on Wednesday as a tropical wave passes
just to the south. This may bring some shower and thunderstorm
activity to mainly the southeastern and central sections of the
A mid to upper level trough stretches from well north of the area
southwestward to 32N70W and to the central Bahamas. Broad
mid/upper ridging is east of the trough to 53W. A large upper
level low near 24N49W is moving westward. Its broad circulation
covers the area north of 19N between 43W-53W. Scattered showers
and isolated thunderstorms are noted from 20N-26N between 47W-53W.
They are moving westward. At the surface, broad surface ridge
anchored by a 1025 mb high centered near 32N58W, and a 1032 mb
high well northeast of the area near 37N29W. A trough extends from
near 31N52W to 26N55W. Isolated showers are within 60 nm of the
trough. Scattered showers and thunderstorms are expected to
develop again over much of the northwestwestern portion of the
area today and continue into this evening.
In the tropical Atlantic, four tropical waves are moving across
that portion of the discusion area. See above for discussions on
these features. Aside from shower and thunderstorm activity
associated with the tropical waves, the remainder of the basin is
under very stable and dry air derived from the Saharan Air Layer
that is present there. These conditions are expected to change
very little through mid-week.
For additional information please visit