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Atlantic Tropical Weather Discussion

AXNT20 KNHC 181804

Tropical Weather Discussion
NWS National Hurricane Center Miami FL
204 PM EDT Sat Aug 18 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 1200 UTC surface analysis and satellite imagery through 
1745 UTC.


A tropical wave is in the E Atlc with axis extending from 07N-18N
along 23W, moving W at 10 kt. The wave is in a strong deep layer
environment and is being affected by dry and dust air intrusion 
in the lower levels as depicted in GOES-16 water vapor and
enhanced IR imagery. These factors are hindering the development
of convection at the time.

A tropical wave is in the central Atlc with axis extending from 
08N-20N along 39W, moving W at 15 kt. The wave is entering a low
deep layer wind shear environment, however is being severely
affected by Saharan dry air and dust, which hinder convection at
the time.

A tropical wave is in the E Caribbean with axis extending from 
07N-18N along 62W, moving W at 15 kt. Both CIRA LPW and GOES-16
water vapor imagery show the northern wave environment being
affected by low level dry air, which is limiting the convection to
scattered moderate across the Windward Islands and SE Caribbean S
of 14N E of 65W.

A tropical wave is in the western Caribbean with axis extending 
from 09N-20N along 79W, moving W at 15 kt. The wave is in a
moderate to strong deep layer wind shear environment and mostly a
dry enviromnent. Shallow moisture in the northern wave environment
and diffluent wind aloft support scattered showers and tstms from
18N-21N between 76W-81W. 


The monsoon trough extends from the coast of W Africa near 09N13W
to 06N26W to 10N40W. The ITCZ begins near 10N40W and continues to
08N50W to 10N58W. Besides the convection mentioned in the 
tropical waves section, scattered heavy showers and tstms are off
the W coast of Africa from 06N-14N E of 20W.



The Bermuda high extends a ridge axis SW across Florida and the 
entire Gulf reaching also eastern Mexico. The ridge is providing 
return flow in the range of 5-10 kt across the region except in 
the north-central Gulf where scattered heavy showers and tstms 
enhance the wind to fresh. The area of convection is N of 27N 
between 85W and 93W and is being supported by inflow of shallow 
moisture from the Caribbean by southeasterly wind and middle level
diffluent flow. Surface ridging will prevail across the basin 
through Wed. Showers over the N-central and NE basin are forecast
to continue through Sun morning.


GOES-16 water vapor imagery at the lower levels show generally
dry, stable air across the basin. Besides dry air, moderate to
strong deep layer wind shear cover the western half of the
Caribbean, thus limiting the areas of convection. A tropical wave
moving S of eastern Cuba support scattered showers over central
and eastern Cuba adjacent waters. Another tropical wave moves
across the E Caribbean supporting showers in the SE basin. See the
tropical waves section for further details. CIRA LPW imagery show
regions of abundant shallow moisture in the basin that support
isolated showers in the Gulf of Honduras and N of 14N between
69W-73W, including Hispaniola. Otherwise, surface ridging 
extending from the Atlantic to the northern half of the basin, 
continues to support fresh to strong winds in the south-central 
Caribbean. The center of high pressure SW of the Bahamas will 
stall the next several days, which will allow the continuation of 
these winds in the south-central basin. Showers will prevail in 
the SE Caribbean through Sunday.


The Bermuda high and the Azores high covers most of the Atlc ocean
mainly supporting fair weather. A weakness in the ridge is
analyzed as a surface trough that extends from 30N54W SW to 
27N60W. Scattered showers and tstms are within 120 nm either side
of the trough. Isolated showers are across the Bahamas. For 
further information associated with the tropical waves, see 
section above.

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