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Atlantic Tropical Weather Discussion

AXNT20 KNHC 172358

Tropical Weather Discussion
NWS National Hurricane Center Miami FL
757 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 1800 UTC surface analysis and satellite imagery through 
2315 UTC.


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.


A tropical wave is over far western Africa with its axis 
extending from 20N17W to 06N17W. 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 22N49W to 15N51W to
07N52W, 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,
to well inland W Africa including the environment of the tropical
wave that is analyzed from 19N16W to 10N16N to 05N16.5W as 
described above.

A tropical wave axis over the central Caribbean extends from
central Cuba at 22N78W to S of Panama at 06N78W, 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 Panama. 


The monsoon trough axis extends from W Africa along the coast of 
Mauritania near 18N16W southwestward to 09N22W to 07N30W, where 
latest scatterometer data indicates that the ITCZ begins and 
continues to 09N50W. The ITCZ resumes west of a tropical wave at 
10N53W and continues to Venezuela near 09N60W. Scattered moderate
convection is from 07N-09N between 22W-26W. Similar convetion is
from 03N-06N between 33W-44W.



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 activity is associated with the tail end
of a mid-level trough that extends to over the northeast and 
north- central gulf waters, with additional support from upper-
level disturbances that are riding NE-SW across the eastern 
periphery of a mid to upper-level anticyclone that situated over 
northeastern Texas. The activity is expected to remain active over
the next 24-48 hrs. 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.


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. 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 develop over
the interior sections of Hispaniola each afternoon through Thu.


A weak surface trough over the western Atlantic extends from near
32N58W to 30N62W. 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. A 1032 mb high is well north of the area near 38N41W.  
Scattered showers and thunderstorms are north of 30N between 75W-
80W are associated with a mid/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 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. 

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