Atlantic Tropical Weather Discussion (Text)

AXNT20 KNHC 171658

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.


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 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.


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.



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.


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.


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


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Page last modified: Tuesday, 17-Jul-2018 16:58:52 UTC