Atlantic Tropical Weather Discussion (Text)

AXNT20 KNHC 211806

Tropical Weather Discussion
NWS National Hurricane Center Miami FL
206 PM EDT Sat Oct 21 2017

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 
1745 UTC.


A tropical wave is in the central Atlc with axis extending from
20N46W to 10N48W, moving W at 20 kt. Satellite derived data 
indicate the wave is in a strong vertical wind shear environment. 
CIRA LPW imagery show abundant dry air in the majority of the 
wave environment at the lower levels. Enhanced IR imagery show
Saharan dry air and dust in the wave environment as well. The
aforementioned environment hinders convection at this time.

A tropical wave is in the western Caribbean with axis extending 
from 20N80W to 09N79W, moving W at 20 kt. The wave is in a region
of low to moderate vertical wind shear. However, deep layer 
moisture along with upper level divergence support scattered 
heavy showers and tstms from 13N-20N between 75W-86W.

A tropical wave is across Central America with axis extending 
from 21N86W across western Honduras to EPAC waters near 08N88W, 
moving W at 20-25 kt. The wave is in a region of moderate to
strong vertical wind shear and shallow moisture. Middle level 
diffluence support scattered showers from 16N-20N between 86W-89W.


The monsoon trough extends from the African coast near 08N13W to 
07N20W. The Intertropical Convergence Zone axis extends from 
07N20W to 06N34W to 06N48W. Scattered moderate convection is from
04N-10N between 32W-42W. 



Middle to upper level ridging prevails across the eastern half of
the Gulf while a trough aloft covers the western half of it.
Diffluent flow between these two features along with shallow
moisture support scattered showers and isolated tstms E of 90W.
Strong dry air subsidence from aloft support clear skies W of 90W. The
SW periphery of a broad surface ridge anchored over the NE CONUS 
covers the NE Gulf and provides the Gulf with moderate to fresh 
return flow E of 90W. Gentle to moderate return flow is elsewhere. Return
flow is expected to continue through Sunday afternoon. The wind
flow will then change as a cold front enters the NW basin Sunday
night and a tropical wave moves across the southern Gulf waters.
Gale force winds are forecast to develop behind the cold front


Two tropical waves underneath an upper ancticylcone are the
drivers of the weather in the western Caribbean W of 75W along
with the eastern extension of the monsoon trough. Strong dry air
subsidence covers the remainder basin supporting fair weather.
However, a plume of Saharan dry air and dust is spread across
Puerto Rico, Hispaniola and the Leeward Islands, thus decreasing
the air quality and reducing visibility. Otherwise, strong high
pressure N of the area continue to support fresh to strong trades
in the central and E Caribbean. A tropical wave will enter the E 
Caribbean Sunday morning and mover across Puerto Rico Tuesday.


Cloudiness and possible isolated showers are mainly across the
western half of the Island while a plume of Saharan dry air and 
dust is spread across the remainder Hispaniola, thus decreasing 
the air quality and reducing visibility. Similar conditions
expected tomorrow Sunday.


A weakening stationary front extends from 30N56W to 25N67W to 
26N77W. Isolated showers are within 200 nm either side of the 
front. Strong high pressure centered NE of the Azores covers the
remainder basin.

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Page last modified: Saturday, 21-Oct-2017 18:06:42 UTC