[Tropical] Tropical Weather Discussion

[EMWIN Server]

AXNT20 KNHC 171658
TWDAT

Tropical Weather Discussion
NWS National Hurricane Center Miami FL
1258 PM EDT Tue Jul 17 2018

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
1600 UTC.

...SPECIAL FEATURES...

SW Caribbean Sea gale warning: The pressure gradient is forecast
to tighten between strong central Atlantic high pressure and
broad low pressure over the southwestern Caribbean Sea beginning
late Wed night increasing the present ongoing strong NE-E winds
over the area from 11N-15N between 70W-77W, including the waters
along the coast of Colombia, to increase to minimal gale force.
These winds will weaken to just below gale force in the early
morning hours of Thu. Seas are expected to build to the range of
10-14 ft with the gale force winds, then subside to 8-11 ft Thu
morning. Please read the High Seas Forecast, under the AWIPS/WMO
headers HSFAT2/FZNT02 KNHC, for more details.

...TROPICAL WAVES...

A tropical wave is over far western Africa with its axis
extending from 19N16W to 10N16W to near 05N16.5W. It is moving
westward near 13 kt. A well defined 700 mb trough is noted in the
model guidance over far western Africa. Latest satellite imagery
is showing increasing cloudiness along with convection in the
vicinity of the wave. The observed cloud pattern is more typically
characteristic of the presence of an ongoing W African monsoon
trough, with the wave passing through it. The imagery shows
scattered moderate convection within 120 nm east and 60 nm west of
the wave from 08N-10N. A major outbreak of Saharan Air Layer
(SAL) dust envelops the wave environment north of 10N as seen in
GOES-16 images.

A central Atlantic tropical wave has its axis along a position
from near 23N45W to 16N48W to near 08N51W, moving westward at
15-20 kt. The wave is depicted on GOES-16 RGB imagery as having a
rather broad inverted-V shape envelope of broken to overcast
stratocumulus clouds covering the area from 09N-23N between 38W-
57W. The wave is being intruded upon by Saharan dust limiting
significant convection from developing near it. Only scattered
showers and isolated thunderstorms are seen within 180 nm to the
east of the wave from 10N-12N, while isolated showers are within
30 nm of a line from 16N47W to 15N50W. The GOES-16 RGB images of
the far eastern Atlantic are depicting yet another massive plume
of Saharan dry air and associated dust following in behind the
wave from 08N-27N east of the wave, to well inland W Africa
including the environment of the tropical wave that is analyzed
from 19N16W to 10N16N to 16.5W as described above.

A tropical wave axis over the central Caribbean extends from
eastern Cuba to 15N77W and inland to the Panama/Colombian border
near 07N745, moving westward around 20 kt. Saharan dust is
following in behind this wave axis as observed in GOES-16
satellite imagery. No deep convection is presently noted with this
wave over the Caribbean waters. The earlier noted scattered
moderate to strong convective activity has shifted westward to
Panama and weakened to scattered moderate convection over central
Panama and its immediate adjacent waters. Isolated showers are
possible elsewhere within 60-90 nm of the wave axis.

...MONSOON TROUGH/ITCZ...

The monsoon trough axis extends from W Africa along the coast of
Mauritania near 19N16W southwestward to 11N20W and to 07N30W,
where latest scatterometer data indicates that the ITCZ begins and
continues to 09N39W to 09N49W. It resumes west of the above
described tropical wave at 09N51W and to 07N59W. Scattered
moderate convection is within 120-180 nm east-southeast of the
trough between 18W-21W. Similar activity is also within 60 nm
south of the ITCZ between 32W-37W, and within 30 nm of a line
from 06N38W to 05N45W.

...DISCUSSION...

GULF OF MEXICO...

The western periphery of Atlantic high pressure ridging extends
E to W over the central gulf waters.Light to moderate
anticyclonic flow are over the gulf waters. Current NWS mosaic
radar shows scattered moderate convection over the northern gulf
north of 28N between 88W-91W. Isolated showers and thunderstorms
are over the remainder of the gulf waters. Expect rather weak
high pressure to prevail across the northern gulf waters through
Thu. A surface trough will move westward off the Yucatan Peninsula
each evening through Thu, enhancing nocturnal winds over the
eastern section of the SW Gulf.

CARIBBEAN SEA...

Please read the Special Features section for details about the
next pulsing gale force wind event in the far SW Caribbean near
the coast of Colombia. Aside from the tropical waves mentioned
above, a small upper-level low is seen on water vapor imagery over
the extreme northeastern part of the Yucatan Peninsula, with a
shear axis stretching from it eastward to east-central Cuba and to
the SE Bahamas. Mainly fresh E winds will continue over the
central Caribbean Sea and strong NE-E winds will be over the SW
and S central sections of the Caribbean through Thu. Low-cloud
streamers with brief isolated showers will continue over the far
eastern Caribbean through Thu. Scattered showers and thunderstorms
will develop over the interior sections of Hispaniola each
afternoon through Thu.

ATLANTIC OCEAN...

A weak surface trough over the western Atlantic extends from near
32N61W to 30N63W. Scattered showers and isolated thunderstorms
are ahead of the trough from 27N to 32N between 55W-59W and also
from 28N-30N between 59W-61W. The trough will dissipate Wed as
the supporting upper trough continues to lift northeastward
away from it. High pressure will build in the wake of the trough.
A large area of Saharan Air Layer (SAL) dust that is currently
over the central Atlantic from 09N-24N and between 48W- 65W will
continue to translate westward through the rest of the week. A
more subtle batch of dust tracking westward is observed from 18N-
27N between 60W and the Bahamas. It spreads southwestward to over
much of Cuba, with some of it spreading westward through the
Straits of Florida.

For additional information
please visit http://www.hurricanes.gov/marine

$$
Aguirre
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