Tropical Weather Discussion

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Tropical Weather Discussion (NHC/TPC):
NWS National Hurricane Center Miami FL
804 AM EDT Tue Jul 17 2018

Corrected first paragraph under the Tropical Waves section

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 0600 UTC surface analysis and satellite imagery through 
1145 UTC.

...SPECIAL FEATURES...

SW Caribbean Sea gale warning: The pressure gradient is forecast 
to tighten between strong central Atlantic high pressures 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...Corrected

A tropical wave was identified yesterday to be moving through 
western Africa, and as of 0600 UTC this morning its axis was 
analyzed along 15W from 03N-16N, moving westward around 15 kt. A 
well defined 700 mb trough is noted together with an inverted-V 
pattern in its associated cloud/convection structure. Scattered 
moderate isolated strong convection is ahead of the wave from 
08N-12N between 17W-20W. Saharan dust is noted on GOES-16 
imagery behind and around this tropical wave.

A central Atlantic tropical wave extends along a position from 
near 20N45W to 14N47W to 06N48W, 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 from 09N-22N between 38W- 53W. Scattered 
moderate convection is seen within 120 nm to the west of the 
wave from 14N-17N, and within 180 nm east of the wave from 06N-
07N. Scattered showers and isolated thunderstorms are within 180 
nm to the west of the wave from 10N-14N. 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 09N-27N east of 36W to well inland of W Africa.

A tropical wave axis over the central Caribbean extends from just
west of Haiti to 15N75W to inland NW Colombia near 07N745, moving
westward at 20 kt. This wave has Saharan dust following the wave 
axis as observed in GOES-16 satellite imagery. No deep convection
is presently noted with this wave over the Caribbean waters.
Scattered moderate to strong convection is being enhanced over 
NW Colombia, including its nearby coastal waters from 07N-10N
between 74W-78W. Isolated showers are possible elsewhere within
60-90 nm of its axis.

A tropical wave pulling farther away from the region has its axis
roughly along 91W S of 20N, moving westward at 10-15 kt. Only 
isolated showers and thunderstorms are noted within 90 nm east of 
this wave over northern and central Guatemala. Future details on 
this wave will be described in the eastern Pacific Tropical 
Weather Discussion. 

...MONSOON TROUGH/ITCZ...
     
The monsoon trough extends from W Africa near 18N16W to 10N21W to
07N30W, where latest scatterometer data indicates that the ITCZ 
begins and to 09N40W to 09N46W. It resumes west of the above 
described tropical wave at 08N49W to 06N55W. Scattered moderate 
isolated strong convection is within 240 nm southeast and south of
the trough between 17W-20W. Scattered moderate convection is 
within 60 nm south of the ITCZ between 28W-34W, and also south of 
the ITCZ within 30 nm of 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
pulsing gale force winds near the coast of Colombia. Aside from 
the tropical waves mentioned above, an upper level low is noted 
on water vapor imagery just to the south of the Yucatan Channel.
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.

ATLANTIC OCEAN...

A weak surface trough over the W Atlantic extends from 32N59W to 
29N65W. Scattered showers and isolated thunderstorms are within 
60 nm of the trough. This trough will slowly weaken Tue as the 
supporting upper trough lifts to the NE 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 45W-60W will continue to 
translate westward through the rest of the week. A more subtle 
batch of dust tracking westward is observed from 09N-27N between 
60W and the central 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

$$
Graphical representation of waves, etc. on this image (NCEP/OPC) [more].
Various tropical satellite imagery available here

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