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Atlantic Tropical Weather Discussion

AXNT20 KNHC 180543

Tropical Weather Discussion
NWS National Hurricane Center Miami FL
143 AM EDT Wed Jul 18 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 0000| UTC surface analysis and satellite imagery through
0515 UTC.


SW Caribbean Sea gale warning: A gale is in effect along the coast
of Colombia from 11N to 13N between 70W and 76W, with seas 8 to 13
ft. The gale ends on 18/1200 UTC. The gale resumes on 19/0000 
UTC, and ends again 19/1200 UTC. Please read the High Seas 
Forecast, under the AWIPS/WMO headers HSFAT2/FZNT02 KNHC, for more


A tropical wave is just off the coast of W Africa with axis 
extending from 20N18W to 07N20W. 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 and 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 extends from 22N51W to 14N54W to
07N55W, 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 43W-60W. 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 
16N51W to 16N55W. 

A tropical wave axis over the central Caribbean extends from
W Cuba at 22N82W to S of Panama at 06N81W, moving westward at 20 
kt. Saharan dust is following in behind this wave axis as observed
in GOES-16 satellite imagery. Scattered moderate to isolated 
strong convection is over Central America from from Honduras to 


The monsoon trough axis extends from W Africa near 20N16W to 
07N30W to 06N36W, where latest scatterometer data indicates that 
the ITCZ begins and continues to 08N45W to 10N53W. The ITCZ 
resumes west of a tropical wave at 10N56W and continues to South
America near 09N60W. Scattered moderate convection is from 07N- 
09N between 24W-30W. Similar convetion is from 03N-06N between 



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 isolated strong convection over 
the northern gulf north of 28N between 86W-92W. Scattered 
moderate convection is over the far northeastern waters north of 
28N and east of 84W. This convection is expected to remain for the 
next 24 hrs. Expect rather weak high pressure to prevail across 
the northern gulf waters through Thu. A surface trough will move 
westward off the Yucatan Peninsula Thu evening, enhancing 
nocturnal winds over the eastern section of the SW Gulf.


Please read the Special Features section for details about the 
pulsing gale force wind events 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. Mostly 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 again develop over the 
interior sections of Hispaniola Thu afternoon.


A weak surface trough over the western Atlantic extends from near
32N57W to 29N60W. Scattered showers are within 60 nm of the trough
axis. The trough will dissipate tonight as the supporting upper 
trough continues to lift northeastward. A 1032 mb high is well 
north of the area near 38N41W. Scattered showers and thunderstorms
are north of 28N between 70W-80W due to an upper level trough 
that stretches along the U.S. eastern seaboard. This activity will
remain active through Thu as a strong deep-layer trough moves off
the eastern seaboard. High pressure will build in the wake of this
trough. A large area of Saharan Air Layer (SAL) dust is currently
over the central Atlantic from 09N-24N and between 48W-65W. The
dust will continue to translate westward for the rest of the 
week. A more subtle batch of dust tracking westward is observed 
from 18N-27N between 60W and the Bahamas. 

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