Tropical Weather Discussion
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AXNT20 KNHC 171020

Tropical Weather Discussion
NWS National Hurricane Center Miami FL
620 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 0600 UTC surface analysis and satellite imagery through
1015 UTC.


Hurricane Gert is centered near 41.7N 54.0W at 17/0900 UTC or
about 300 nm S of Cape Race Newfoundland moving ENE at 34 kt.
Estimated minimum central pressure is 968 mb. Maximum sustained
wind speed is 85 kt with gusts to 105 kt. Numerous moderate
convection and scattered tstms are from 40N-44N between 50W-55W.
Scattered moderate convection is elsewhere from 40N-48N between
45W-55W and from 35N-39N between 54W-60W. See latest NHC
forecast/advisory under AWIPS/WMO headers MIATCMAT3/WTNT23 KNHC
for more details.

A 1008 mb low is located about 475 nm east of the Lesser Antilles
near 13N52W. Intrusion of Saharan dry air and dust to its
environment is observed in GOES-16 experimental imagery and CIRA
LPW imagery, however the system continue to show signs of
organization. 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. 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 14N40W. The wave axis extends from
21N40W 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 NW quadrant 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 1010 mb low
near 08N21W. The wave axis extends from 16N21W to the low center
to 04N21W. 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 16N E of 29W.
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
21N65W to 11N69W, moving W at 15-20 kt. There is abundant
moisture associated with this wave that along with upper level
divergent flow support scattered moderate convection and tstms
from 16N-24N between 61W-71W, including Puerto Rico.

A tropical wave is in the Yucatan Peninsula with axis extending
from 21N87W across Belize and Guatemala to 11N89W, 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 13N16W to
08N21W to 08N33W. 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 04N-09N
between 30W-46W.



Except for isolated showers and tstms within 60 nm of Veracruz,
Mexico supported by middle level diffluent, the remainder basin
in under the influence of a surface ridge anchored by a 1017 mb
high near 27N85W. This setup is providing ESE gentle to moderate
flow across the Gulf, except for fresh winds off the Texas coast
and light to gentle variable flow in the NE basin around the high
center. 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 Yucatan Peninsula, Belize
and Guatemala supporting isolated showers. A second tropical wave
is in the E Caribbean with axis near 68W, which is supporting
scattered showers and tstms over the N and NE basin including
Puerto Rico, the Virgin Islands and Dominican Republic adjacent
waters. See tropical waves section for further details.
Generally, diffluent flow is observed in the SW Caribbean, which
is supporting numerous heavy showers and tstms from 09N-12N
between 80W-84W. 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 isolated showers
across central Cuba. Otherwise, dry air subsidence and strong
vertical 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
today with moderate to fresh trades elsewhere.


An upper level low is centered N of the Windward Passage ahead
of a tropical wave that is forecast move over the central
Caribbean later this morning. The approaching wave is already
supporting scattered showers and tstms over the Dominican
Republic adjacent waters and isolated showers inland, but this
activity will increase through the course of the day into Friday.


Except for the SW N Atlc waters that are being impacted by the
tropical wave moving to central Caribbean waters later this
morning, the remainder basin generally N of 20N is under the
influence of the Azores subtropical high which supports fair
weather. Otherwise, see special features and tropical waves sections

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