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Active Tropical Systems Tropical Season Archive Satellite National Hurricane Center
Outlooks Discussions Tropical Summaries  
Tropical Atlantic Discussion  Tropical Eastern Pacific Discussion

AXNT20 KNHC 201740

Tropical Weather Discussion
NWS National Hurricane Center Miami FL
140 PM EDT Fri Oct 20 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
20N35W to 08N41W, moving W at 10-15 kt. Satellite derived data 
indicate the wave is in a strong vertical wind shear environment. 
CIRA LPW imagery show dry air in the majority of the wave 
environment. The wave is underneath diffluent flow aloft between 
an upper low centered near 21N41W and a ridge over the tropical 
eastern Atlc. This is supporting scattered moderate convection 
from 13N-22N between 33W-40W.

A tropical wave is in the central Caribbean with axis extending 
from 20N72W to 11N73W, moving W at 5 kt. The wave is in a region 
of strong vertical wind shear. However, deep layer moisture along
with upper level diffluent flow between the base of an upper
trough in the SW Atlc and an anticyclone in the W Caribbean
support scattered heavy showers and isolated tstms from 13N-20N 
between 71W-78W.

A tropical wave is in the western Caribbean with axis extending 
from 21N80W to adjacent waters of Costa Rica near 09N82W, moving 
W at 20 kt. The wave is in a region of low to moderate vertical 
wind shear and CIRA LPW imagery show abundant moisture in its 
low to middle level environment. However, the wave is underneath
a broad upper level high, which associated subsidence limits the
convection to isolated showers W of 78W.


The monsoon trough extends from the African coast near 07N12W to 
06N19W. The Intertropical Convergence Zone axis extends from 
06N19W to 04N30W to 07N39W. Scattered moderate convection is 
from 02N-09N E of 17W, from 06N-09N between 26W-36W and from
07N-12N W of 48W.



Middle to upper level ridging prevails across the Gulf E of 93W
while an upper level trough extends from the southern Plains to a
base over the western Bay of Campeche. The troughing aloft 
supports scattered heavy showers and tstms over Louisiana adjacent
waters N of 27N between 91W-95W and between 90W-93W just east of a
surface trough that extends from 25N94W to 17N94W. Strong dry air
subsidence across the basin supports fair weather elsewhere. The 
southern periphery of a broad surface ridge anchored over West 
Virginia by a 1027 mb high covers the remainder northern half of 
the Gulf. The gradient between high pressure to the N and lower
pressure associated with the trough in the SW basin continue to
support moderate to occasional fresh NE to E winds N of 22N E of
90W and SE flow of the same magnitude in the NW Gulf. By 
Saturday, moderate to fresh E-SE flow will re-establish itself 
across the Gulf as an area of low pressure develops across the 
central Plains. Return flow is expected to continue through Sunday


An upper level anticyclone is centered over the western Caribbean
near 18N82W providing an overall divergent environment W of 70W. 
The divergence along with two tropical waves moving across the 
basin are generating scattered showers and tstms from 11N-20N W of
72W, including inland portions of Central America, Jamaica and SW
Haiti. Plenty of atmospheric moisture in associated with the 
ridge and will likely continue to produce relatively active 
convection through the weekend. Otherwise, fresh to strong trades
prevail E of 80W as the pressure gradient strengthens while 
strong high pressure moves off the Mid-Atlc coast and into the 
western North Atlc. The trades are expected to remain strong 
through Monday night.


A tropical wave is moving across Haiti today bringing scattered 
showers and tstms to the SW portions of the island and the 
Windward Passage. Fresh to strong trades are expected through the
weekend as high pressure builds in N of the region.


A cold front extends SW from a 1007 mb low centered near 34N60W
continuing along 30N63W to 25N71W then dissipating to the central
Bahamas near 23N74W. Scattered showers prevails within 150 nm E of
the cold front. This system is supported aloft by a middle-level
low and reinforced by an upper level trough. The remainder of the
eastern Atlc is under the influence of a surface ridge anchored 
by a 1031 mb high centered near 40N38W.

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