AXNT20 KNHC 170605

Tropical Weather Discussion
NWS National Hurricane Center Miami FL
205 AM EDT Thu Aug 17 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 0000 UTC surface analysis and satellite imagery through
0545 UTC.


Hurricane Gert is centered near 40.1N 58.4W at 17/0300 UTC or
about 350 nm SE of Halifax Nova Scotia and about 460 nm SSW of
Cape Race Newfoundland moving ENE at 32 kt. Estimated minimum
central pressure is 967 mb. Maximum sustained wind speed is 90 kt
with gusts to 110 kt. Numerous moderate convection and scattered
tstms are from 37N-42N between 54W-59W. Scattered moderate
convection is elsewhere from 36N-46N between 50W-60W. See latest
NHC forecast/ advisory under AWIPS/WMO headers MIATCMAT3/WTNT23
KNHC for more details.

A 1011 mb low is located about 560 nm east of the Lesser
Antilles near 13N50W. Intrusion of Saharan dry air and dust to its
environment is noticed in GOES-16 experimental imagery and CIRA
LPW imagery, however the system looks a little more concentrated.
This being favored in part by low vertical wind shear. Scattered
moderate convection and isolated tstms are within 220 nm W
semicircle from low center. Isolated showers are within 220 nm SE
quadrant of the low. Upper-level winds are forecast to become
more conducive for development during the next day or so while the
low moves westward across the tropical Atlantic Ocean, crossing
into the Caribbean Sea on Friday. Regardless of development,
locally heavy rainfall and gusty winds are expected to spread
across portions of the Lesser Antilles on Thursday night and
Friday. This system has a medium chance of becoming a tropical
cyclone in the next two days.

A tropical wave is in the central Atlc associated with a 1009 mb
low pressure located near 14N38W. The wave axis extends from
21N38W to the low and has been moving W at 15 kt. The wave is in
a region of low to moderate vertical wind shear, however intrusion
of Saharan dry air and dust to the wave environment limit
convection to scattered moderate within 245 nm W semicircle of
low pressure center. Gradual development of this system is
possible during the next few days while it moves WNW, but upper-
level winds are expected to become less conducive for tropical
cyclone formation when the disturbance moves north of the Leeward
Islands this weekend. This system has a medium chance of becoming
a tropical cyclone in the next two days.


A tropical wave is in the E Atlc associated with a 1013 mb low
near 08N20W. The wave axis extends from 18N18W to the low center.
The CIRA LPW imagery show dry air intrusion to the wave
environment, which has significantly reduced the convection this
wave had when it was coming off the W African coast yesterday.
GOES-16 experimental and Meteosat SAL imagery show Saharan dust
and dry air engulfing this wave. Monsoon moisture and middle to
upper level diffluent flow support scattered moderate convection
and isolated tstms from 06N to 15N E of 25W. Environmental
conditions are forecast to become more conducive for development
over the weekend while the system moves WNW.

A tropical wave is in the E Caribbean with axis extending from
23N61W to 12N66W, moving W at 15-20 kt. There is abundant moisture
associated with this wave that along with upper level divergent
flow support scattered to isolated moderate convection and tstms
from 16N to 24N between 61W and 69W, including Puerto Rico.

A tropical wave is in the W Caribbean with axis extending from
19N85W across Honduras to 10N87W, moving W at 20 kt. The wave is
in a region of low vertical wind shear, however dry air
subsidence continue to limit convection to isolated showers within
90 nm of its axis.


The monsoon trough extends from the African coast near 11N16W to
09N30W. To the west, the monsoon trough and ITCZ is disrupted due
to the tropical lows and tropical waves mentioned above.
Otherwise, scattered moderate convection is from 05N-09N between



Except for scattered showers over the E Bay of Campeche associated
with a surface trough along 93W, the remainder basin in under the
influence of a surface ridge anchored by a 1019 mb high near
28N85W. This setup is prividing ESE gentle to moderate flow across
the northern half of the Gulf, except for light to gentle variable
flow in the NE basin around the high center. Otherwise, NE fresh
winds are off the W Yucatan Peninsula coast associated with the
surface trough. The high is expected to persist across the NE
Gulf waters through early Saturday. A surface trough will develop
each evening across the Yucatan peninsula shifting W into the Bay
of Campeche during the overnight hours. Locally higher winds can
be expected in the vicinity of the trough axis.


A tropical wave is moving across the NW basin and Honduras
supporting isolated showers. A second tropical wave is in the E
Caribbean with axis near 64W, which is supporting scattered to
isolated showers and tstms over the NE basin including Puerto
Rico, the Mona Passage and the Virgin Islands. See tropical waves
section for further details. Genearally, diffluent flow is
obserseved in the SW Caribbean, which is supporting scattered
showers S of 13N W of 70W. Lastly, a diffluent flow pattern
persist between an upper level ridge anchored over S Georgia and a
low centered N of the Windward Passage. This continue to support
scattered to isolated showers across central Cuba. Otherwise, dry
air subsidence and strong vetical wind shear support fair weather
elsewhere W of 70W. Fresh to strong winds in the south-central
waters and in the vicinity of the tropical wave in the eastern
waters are expected through Thursday with moderate to fresh trades


An upper level low is centered N of the Windward Passage ahead
of a tropical wave that is forecast move over the central
Caribbean Thursday. The approaching wave is already supporting
isolated showers over the Dominican Republic, but the activity
will increase during Thursday and into early Friday.


The basin N of 23N continue under the influence of the Azores
subtropical high which supports fair weather. For information
about tropical waves, see sections above.

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