NHC Atlantic Tropical Weather Discussion

AXNT20 KNHC 041156 RRA

Tropical Weather Discussion
NWS National Hurricane Center Miami FL
550 AM EDT Mon Sep 4 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
1115 UTC.


Hurricane Irma is centered near 16.8N 52.6W at 04/1200 UTC or
about 473 nm E of the Leeward Islands moving WSW at 12 kt.
Estimated minimum central pressure is 947 mb. Maximum sustained
wind speed is 105 kt with gusts to 130 kt. Numerous strong
convection is from 15N to 19N between 50W and 54W. Scattered
moderate convection is elsewhere from 13N to 20N between 47W and
56W. The center of Irma is expected to approach the northern
Leeward Islands late Tuesday. Some strengthening is forecast
during the next 48 hours. See the latest NHC Intermediate Public
Advisory under AWIPS/WMO headers MIATCPAT1/WTNT31 KNHC and the
full Forecast/ Advisory under AWIPS/WMO headers MIATCMAT1/WTNT21
KNHC for more details.


A tropical wave came off the W African coast earlier today. Its
axis extends from 18N18W to 07N16W and is forecast to move W at
10 kt within the next 24 hours. The wave is in a region of low
vertical wind shear and CIRA LPW imagery show patches of dry air
in the northern wave environment N of the monsoon trough.
Shallow moisture along middle to upper level diffluence support
scattered moderate convection from 05N to 12N E of 18W.

A tropical wave is in the central Atlc associated with a 1011 mb
low located near 10N33W. The wave axis extends from 17N33W to the
low to 08N33W and it has been moving W at 10 kt. The wave is in a
region of low to moderate vertical wind shear, however enhanced
IR imagery continue to show some Saharan dry air and dust in the
wave environment. CIRA LPW imagery at the lower levels confirm
the presence of dry air in the vicinity of the wave. Shallow
moisture and divergence aloft support scattered moderate
convection from 04N to 14N between 30W and 41W. Environmental
conditions are expected to be conducive for gradual development,
and a tropical depression will likely form later this week while
the system moves west-northwestward over the tropical Atlantic

A tropical wave is in the central Caribbean with axis extending
from 20N74W to 09N76W, moving W at 20-25 kt. The wave is in a
region of low vertical wind shear, however it continues being
affected by dry air subsidence from aloft, except N of 17N where
upper level diffluence support scattered showers and tstms across
Western Haiti, the Windward Passage and Cuba adjacent waters.


The monsoon trough extends from the African coast near 12N16W to
12N28W to 09N39W to 12N42W. Aside from the convection associated
with the tropical waves, scattered moderate convection is from
04N to 10N between 20W and 30W.



Water vapor imagery show an upper level trough extending over the
far NW Atlc waters to a broad base over S Florida. Middle to
upper level diffluent flow prevails in the SE basin, thus
supporting the continuation of scattered to isolated showers S of
27N. A surface trough continues in the SW Gulf, extending from
25N96W to 18N94W, which is generating scattered heavy showers and
tstms W of 91W. This feature is expected to dampen out by late
tonight into early Tuesday. Elsewhere, gentle to moderate
easterly winds prevail with isolated showers occurring across
the NW waters W of 90W. A surface ridge axis is expected to
anchor along 30N Tuesday, gradually slide southward, and weaken
by Wednesday as a weak frontal boundary moves off the Texas and
Louisiana coasts.


Former isolated showers and tstms over the Gulf of Honduras are
moving inland southern Belize. In the SW basin, the E extension
of the EPAC monsoon trough continue to support scattered showers
and tstms S of 12N. Otherwise, upper diffluence above a tropical
wave that moves across central Caribbean waters supports
scattered heavy showers and tstms N of 17N between 68W and 83W,
including the Windward Passage and Cuba adjacent waters. For
further details on the wave, see section above. Water vapor
imagery show dry air aloft across the remainder basin, which
subsidence is supporting fair weather conditions. Otherwise,
moderate to locally fresh trades are basin-wide. Looking beyond
today, major Hurricane Irma is expected to approach the northern
Leeward Islands Tuesday evening and will continue to affect the
NE Caribbean through late Thursday.


Isolated showers are across the Island as a tropical wave
continue to move W over central Caribbean waters. Upper level
diffluence over the northern wave environment support scattered
showers and tstms over NE Dominican Republic adjacent waters and
the Windward Passage. Conditions will gradually improve on
Tuesday as the way continues to move away. Looking ahead,
Hurricane Irma is forecast to pass N of the Island early
Thursday through early Friday. See Special Feature for further


Major Hurricane Irma continue to represent a threat for the NE
Caribbean Tue through early Thursday. See special features for
further details. A middle to upper level trough progressing over
far NW Atlc waters supports isolated showers over the SW North
Atlc W of 75W. Farther east, an upper level low supports a
surface trough extending from 29N66W to 24N68W. Scattered showers
and tstms are E of the surface trough from 22N to 29N between 60W
and 66W. Surface ridging prevails elsewhere N of 24N.

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Source: Atlantic Tropical Weather Discussion