Tropical Weather Discussion

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Tropical Weather Discussion (NHC/TPC):
NWS National Hurricane Center Miami FL
805 AM EDT Wed Sep 26 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 0600 UTC surface analysis and satellite imagery through 
1115 UTC.

...Special Features...

The earlier remnants of Kirk have regenerated back into a
tropical storm as of 0900 UTC this morning. At 0900 UTC Tropical 
Storm Kirk is centered near 11.8N 52.7W, which is about 405 nm
east of Barbados or 515 nm ESE of Martinique, moving westward at 
16 kt. The estimated minimum central pressure is 1004 mb. The 
maximum sustained wind speed is 40 kt with gusts to 50 kt. Latest
satellite imagery shows that deep convection of the numerous 
moderate to strong type intensity has increased near the center of
the tropical cyclone, while at the same time it has gradually 
become symmetrical during the past few hours. This convection is 
observed within 120 nm of the center in the SE semicircle and 
within 90 nm of the center in the NW semicircle. Scattered 
moderate isolated strong convection is to the northeast of 
Kirk from 14N to 16N between 49W and 52W, and from 10N to 13N 
between 53W and 56W. The latest NHC advisory has Kirk moving in a 
westward to west-northwestward motion through Fri night. On this
forecast track, Kirk is expected to approach Barbados and the 
northern Windward Islands Thu afternoon and move into the eastern 
Caribbean Sea by Fri morning. Little change in strength is 
forecast until Kirk moves through the central Lesser Antilles Thu 
afternoon and evening. Rapid weakening is expected on Fri after 
Kirk emerges over the Caribbean Sea. See latest NHC Forecast/Advisory
under AWIPS/WMO Headers MIATCMAT2/WTNT22 KNHC for more details. 

A strong cold front has been added to the analysis over the
central Atlantic extending from an area of low pressure associated
with Post-Tropical Cyclone Leslie north of the area. The cold 
front extends from 31N39W to 28N45W to 28N55W to 29N60W. The 
latest ASCAT data show gales are currently occurring north of 29N 
between 40W-42W. Winds in this area are forecast to diminish below
gale force late this afternoon. However, winds will remain around
30 kt in the area during the next couple of days. Scattered 
moderate convection is along and within 120 nm ahead of the front 
for the portion of the front that's east of 41W. Meanwhile, Post- 
Tropical Cyclone Leslie, centered about 740 nm west-southwest of 
the Azores, is producing gale force winds. Scattered moderate 
convection is from 34N-38N between 37W-42W. Leslie is expected to
reacquire subtropical or tropical characteristics on Thu or Fri 
while the cyclone meanders over the north-central Atlantic. There 
is a medium chance of this system becoming a tropical or 
subtropical cyclone during the next 48 hours. For more information
on this system, see High Seas Forecasts issued by the National 
Weather Service.

...TROPICAL WAVES...

A far eastern Atlantic tropical wave has its axis along 23W from 
03N to 17N, moving westward at 10 to 15 kt. Model guidance depicts
a broad 700 mb trough over or slightly ahead of this wave. The 
satellite-derived low to mid-level winds nicely display a NE to 
SE wind shift across the wave. Satellite imagery shows isolated 
showers and thunderstorms are within 150 nm west and 120 nm east 
of the wave axis from 11N to 15N.

A tropical wave has its axis along 70W south of 19N, moving 
westward at 15 kt. This wave appears to be weakening and losing
definition. However, the Total Precipitable Water (TPW) satellite
animation shows a broad pool of moisture between 65W-70W. 
Scattered showers and isolated thunderstorms are near and east of 
the wave axis between Trinidad and the south coast of the 
Dominican Republic.

...MONSOON TROUGH/ITCZ...

The monsoon trough axis extends off the coast of Africa over
Senegal at 13N17W and continues to 10N23W to 07N31W, where the 
ITCZ begins and continues to 07N41W. Outside of the convection 
mentioned with the tropical wave, scattered moderate convection 
is within 210 nm north and 180 nm south of the ITCZ and monsoon
trough between 29W-41W.

...DISCUSSION...

GULF OF MEXICO...

A very moist and unstable air mass along with upper-level 
diffluence over the north-central Gulf Coast is currently
resulting in scattered showers and thunderstorms north of 27.5N 
between 89W-93W. This activity pulsated up and down last night but
has generally been moving slowly westward. Isolated showers are
near a trough over the NE Gulf within 100 nm offshore of the Big
Bend area of FL.

A thermal trough over the east-central Bay of Campeche is helping
to enhance scattered showers and isolated thunderstorms, currently
seen from 20N-24N between 91W-94W. A surface trough will develop 
over the Yucatan peninsula each evening, shift W over the SW Gulf 
each night, then dissipate each morning. Elsewhere across the 
Gulf, gentle to moderate winds will increase to between moderate 
and fresh during the second half of this week as high pressure 
builds N of the region.

CARIBBEAN SEA...

Convection associated with the tropical wave in the eastern 
Caribbean is described above in the Tropical Waves Section. Most
of the central Caribbean from 71W-80W is free of any significant
convection at this time. Instability generated by the eastern 
Pacific monsoon trough that protrudes into the far southwestern 
Caribbean, along with low-level speed convergence and to some 
extent a weak upper low near 12N80W, which is at the base of an 
upper trough, has resulted in numerous moderate and isolated
strong convection between 81W and the coasts of northern Costa 
Rica, Nicaragua and eastern Honduras. This activity is likely
producing heavy rainfall over eastern Nicaragua and NE Costa Rica. 
Expect fresh to strong winds over the central Caribbean through 
midweek, with moderate to fresh winds thereafter through Friday.

ATLANTIC OCEAN...

The eastern Atlantic tropical wave, Tropical Storm Kirk, Post
Tropical Cyclone Leslie and the cold front bringing gale force
winds to the area have all been described above in the Special
Features and Tropical Waves sections.

A pre-frontal surface trough is analyzed just ahead of the cold
front mentioned above over the central Atlantic. The trough then
extends SW to 25N45W to 20N59W. All convection associated with
this is north of 25N and east of 50W.

Another surface trough extends from 29N30W to 23N31W. Only 
isolated showers are within 60 nm of the trough. Otherwise, 
ridging over the northeast Atlantic is helping to maintain 
generally stable and create fair weather north of 20N and east of 
30W.

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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