Tropical Weather Discussion

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Tropical Weather Discussion (NHC/TPC):
NWS National Hurricane Center Miami FL
805 PM Wed Jul 15 2020

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
2345 UTC.


A far eastern Atlantic tropical wave has its axis along 24W from
02N-19N, moving westward at an estimated speed of about 15 kt. 
This wave is helping to enhance convection along the west African
monsoon trough as evident by the clusters of scattered moderate 
to isolated strong convection that are occurring within 120 nm 
west of the wave axis from 07N to 11N. Scattered moderate 
convection is seen from 05N to 07N west of the wave to 33W.

A central Atlantic tropical wave has its axis along 37W from 
03N to 17N, moving westward at 10-15 kt. This wave is moving 
through a stable surrounding environment. Only scattered showers 
and isolated thunderstorms are noted within 180 nm east and 60 nm
west of the wave axis from 03N to 08N.

Another central Atlantic tropical wave is analyzed with its axis
along 53W south of 20N to inland South America. It is moving
westward at 15-20 kt. Saharan dust was noted in the last few
GOES-16 visible images to be present across this wave. This is
inhibiting any deep convection from developing near the wave for
the time being. Only isolated showers are along and within 150 
nm ahead of the wave axis from 05N-11N.

An eastern Caribbean Sea tropical wave has its axis along 66W
from 11N to 22N. It is moving westward at an estimated speed of
16 kt. Very strong subsidence and resulting dry air over this
area of the Caribbean is only allowing for fast moving isolated 
showers to exist east of the wave and within 180 nm west of the
wave north of 14N.


The monsoon trough axis extends from the coast of Africa near 
13N17W south-southwestward to 09N20W and westward to 09N30W and 
to 08N42W, where latest scatterometer data indicates the ITCZ
begins and continues to 08N48W and to 08N52W. It resumes west
of a tropical wave (position at 53W) from 07N54W to 07N58W. 
Aside from the convection mentioned above in association  
with the tropical waves, overall deep convection is very minimal
along the and near the monsoon trough and ITCZ. Only scattered 
moderate convection is within 60 nm northwest of the monsoon 
trough between 17W-18W.


A mid to upper-level small low is identified on water vapor
imagery to be over the Florida panhandle near 30N86W. A mid to 
upper-level trough extends from the low to near 27N89W. With
these features acting on a very unstable environment in place,
the result has been for clusters showers and thunderstorms near
and inland the coast between Pensacola and southeastern
Louisiana. Isolated showers and thunderstorms are within 60 nm
offshore that same coast. Expect for most of the shower and 
thunderstorm activity to gradually diminish during tonight.

A weak 1019 mb high center is near 26N86W, with weak ridging 
extending from it west-northwest to the northeastern Texas. The 
associated gradient is providing for gentle wind speeds over the 
eastern and central Gulf, with slightly higher winds, of 
moderate speeds, closer to Texas and in the SW Gulf.

As for the forecast. the ridge will lift northward tonight ahead
of a surface trough moving across Florida into the southeast 
Gulf before dissipating over the central Gulf through Sat. This 
pattern will maintain gentle to moderate winds and low seas, 
except for locally fresh winds near the coast of the Yucatan 
peninsula due to local effects. 


A well noted mid to upper-level inverted trough over Central 
America earlier today helped developed numerous moderate to 
isolated strong convection over Nicaragua, and adjacent waters
of the Caribbean within 60 nm of the coast of Nicaragua. 
However, during the past few hours this activity has diminished 
in coverage and in intensity. The combination of Saharan dust and
moderate to subsidence aloft spread throughout just the entire 
basin is keeping the atmosphere very stable limiting deep 
convective activity from forming. The latest scatterometer data 
shows fresh to strong trade winds in the south-central Caribbean,
south of 15N and between 73W-78W.

As for the forecast, high pressure north of the area will 
maintain pulses of fresh to strong winds tonight in the Windward 
Passage, Gulf of Honduras and off Colombia. These winds will 
diminish through Thu as the high shifts farther to the north. 


A mid to upper-level trough stretches from near 32N67W to
29N69W, where it becomes a shear axis to 28N75W and to 
near 30N79W. At the surface, a small surface trough extends from
near 32N74W to 28N77W. A more prominent surface trough extends 
from near 30N69W to just north of the southeastern Bahamas. 
Scattered showers and isolated tstorms prevail across the area 
from 21N-28N between 69W and the coast of Florida, including the 
Bahamas. Farther east, another surface trough is analyzed from 
31N53W to 23N59W. Isolated showers are seen moving quickly 
westward near the trough axis. Yet another surface trough extends
in a SE to NW fashion from near 15N31W to 20N40W. Afternoon 
scatterometer data depicted generally gentle wind speeds across 
most of the area, except for locally fresh speeds in the Windward
Passage. The scatterometer data also highlighted moderate to 
fresh north to northeast winds over the far eastern Atlantic 
north of 24N and east of 24W to the vicinity of the Canary 
Islands. High pressure covers the remainder of the area.

As for the forecast, the two troughs northeast of the Bahamas 
will shift westward and weaken tonight. The trough well east
of the Bahamas will gradually weaken as it moves toward the
northern Bahamas by Sat. Meanwhile, a ridge will build north of 
the area, supporting moderate to fresh trade winds south of 22N 
into early next week. 

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

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