[Tropical] Tropical Weather Discussion

[EMWIN Server]

AXNT20 KNHC 111748
TWDAT

Tropical Weather Discussion
NWS National Hurricane Center Miami FL
148 PM EDT Tue Sep 11 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.

...SPECIAL FEATURES...

Hurricane Florence is centered near 26.4N 64.6W at 11/1500 UTC or
340 nm S of Bermuda and about 790 nm ESE of Cape Fear North
Carolina moving WNW or 295 degrees at 14 kt. The estimated minimum
central pressure is 950 mb. The maximum sustained winds are 115
kt with gusts to 140 kt. Latest satellite imagery shows scattered
moderate to strong convection within 120 nm of the center in the
NE quadrant, and within 120 nm of the center in the SE quadrant.
Scattered moderate convection is within 240 nm of the center in
the NW quadrant, and within 120 nm of the center in the SW
quadrant. Florence is forecast to continue on a west-
northwestward to northwestward motion with a slight increase in
forward speed are expected during the next couple of days. On the
forecast track, the center of Florence will move over the
southwestern Atlantic Ocean between Bermuda and the Bahamas
through Wednesday, and approach the coast of North Carolina or
South Carolina on Thu. Interests elsewhere in the southeastern and
mid-Atlantic states need to monitor the progress of Florence.
Public Advisories for Florence are issued under WMO header WTNT31
KNHC and under AWIPS header MIATCPAT1. Forecast/Advisories for
Florence are issued under WMO header WTNT21 KNHC and under AWIPS
header MIATCMAT1.

Tropical Storm Isaac is centered near 14.6N 49.7W at 11/1500 UTC,
which is about 675 nm E of the Lesser Antilles moving W or 270
degrees at 14 kt. The estimated minimum central pressure is 996
mb. The maximum sustained wind are 60 kt with gusts to 75 kt.
Latest satellite imagery shows scattered moderate to strong
convection within 90 nm of the center in the NW and SE quadrants
and within 120 of the center in the NE quadrant. Scattered
moderate convection is within 30 nm of the center in the SW
quadrant. The present motion is expected to continue through the
end of the week. On is present motion, Isaac is expected
move near or over the central Lesser Antilles on Thu and move
into the eastern Caribbean Sea Thu night. Swells generated by
Isaac will begin to affect portions of the Lesser Antilles on Wed
afternoon. These swells are likely to cause life-threatening surf
and rip current conditions. Please consult products from your
local weather office. Public Advisories for Isaac are issued under
WMO header WTNT34 KNHC and under AWIPS header MIATCPAT4.
Forecast/Advisories for Isaac are issued under WMO header WTNT24
KNHC and under AWIPS header MIATCMAT4.

Hurricane Helene is centered near 16.5N 34.3W at 11/1500 UTC,
which is about 585 nm west of the southernmost Cabo Verde Islands
or 1350 nm south-southwest of the Azores moving NW or 310 degrees
at 10 kt. The estimated minimum central pressure is 966 mb. The
maximum sustained winds are 95 kt with gusts to 115 kt. Latest
satellite imagery shows that Helene's cloud pattern has not
changed much over the psst several hours. Scattered moderate
isolated strong convection is within 180 nm of the center in the
eastern semicircle and SW quadrant, and within 150 nm of the
center in the NW quadrant. Helene is forecast to maintain its
present motion today, with a turn toward north-northwest and
northward thereafter on Wed and Thu. Gradual weakening should
begin tonight, and Helene is forecast to become a tropical storm
on Thu near 22.5N 38.2W. Public Advisories for Helene are issued
under WMO header WTNT33 KNHC and under AWIPS header MIATCPAT3.
Forecast/Advisories for Helene are issued under WMO header WTNT23
KNHC and under AWIPS header MIATCMAT3.

A surface trough extends from the southeastern Gulf of Mexico near
25N84W to inland the eastern Yucatan Peninsula. An upper-level
low is identified to be just north of the Yucatan Peninsula at
23N88W. Satellite visible imagery indicates that a weak surface
low pressure may be forming near 23N87W. The surface trough is
interacting with the upper-level low. Satellite imagery shows
numerous moderate to strong convection convection from 18N to 22N,
including the Yucatan Channel and western half of Cuba from 81W
to 85W. Scattered moderate isolated strong convection is seen from
22N to over the far southeastern Gulf of Mexico near 26N between
82W and 88W, including the western section of the Straits of
Florida. This entire area of convection is gradually becoming
better organized. Ship reports indicate that this system is
producing strong gusty winds over the Yucatan Channel. Upper-level
winds are forecast to become more conducive for development, and
a tropical depression is likely to form by Thu night while the
disturbance moves across the western Gulf of Mexico. If necessary,
an Air Force Reconnaissance plane will investigate the system
tomorrow. This area of disturbed weather has a medium chance for
tropical cyclone formation over the next couple of days. Interests
across northeastern Mexico and the coasts of Texas and Louisiana
should monitor the progress of this system. Regardless of
development, heavy rainfall and gusty winds are expected to
continue over western Cuba and portions of the northeastern
Yucatan Peninsula during the rest of today. Please read the
latest Tropical Weather Outlook under WMO header ABNT20 KNHC, and
under the AWIPS header MIATWOAT for more details on this evolving
system.

...TROPICAL WAVES...

Tropical waves are not presently over water, however, the next
tropical wave expected to move across the discussion area waters
in the short-term is presently over the interior of Africa near
10W. Ahead of this wave, scattered moderate isolated strong
convection is observed from 09N to 13N east of 17W to well inland
the African coast.

...MONSOON TROUGH/ITCZ...

The monsoon trough is non-continuous over the interior of
Africa. The western segment of the trough extends southwestward
from coast of Sierra Leone to 06N18W. The ITCZ is not analyzed
at this time. Scattered moderate convection is within 180 nm
south and 120 nm north of the monsoon trough between 17W and 18W.

...DISCUSSION...

GULF OF MEXICO...

See Special Features above for details on an area of disturbed
weather over the southeastern Gulf of Mexico.

A narrow upper-level trough extends from the northeastern part
of the Gulf of Mexico to the eastern central Gulf of Mexico and
to an upper-level low at 23N88W, It continues from the low to
inland the eastern Yucatan Peninsula. Associated upper cyclonic
flow is present south of 29N and east of 93W. Upper-level
anticyclonic wind flow covers the Gulf of Mexico west of 93W and
the Atlantic Ocean to 70W, and the Caribbean Sea from 15N
northward from 70W westward. Aside from the convection associated
with the above described area of disturbed weather over the
southeastern gulf waters, isolated showers and thunderstorms are
noted elsewhere east of 91W.

A stationary front stretches from southwestern Louisiana to inland
the southern Texas coast. Plenty of deep atmospheric moisture is
present over the far western gulf as a rather strong upper trough
moves across central Texas. Scattered moderate isolated strong
convection is noted north of 22N and west of a line from 30N91W to
25N94W to 22N95W. Scattered showers and isolated thunderstorms
are elsewhere west of 91W.

A surface trough in the western Caribbean Sea will move across
the Yucatan peninsula on Tue, and into the Gulf of Mexico on
Wed. The trough is expected to move into the western Gulf on
Thu and to the west of the area on Sat.

CARIBBEAN SEA...

A surface trough extends from the southeastern Gulf of Mexico near
25N84W to just inland the eastern section of the Yucatan
Peninsula. An upper-level trough extends from an upper-level low
just north of the Yucatan Peninsula south-southwestward to just
inland the peninsula. Plenty of available deep tropical moisture
along with the presence of these features has resulted in plenty
of atmospheric instability, leading to numerous moderate to strong
convection north of 18N and west of 81W, including western Cuba
and the Yucatan Channel. This activity is likely to be accompanied
by strong to near gale gusty winds and very heavy rainfall as it
gradually lifts northward over the eastern and central Gulf of
Mexico through Thu. See Special Features section above for more
details on this area of disturbed weather. Scattered showers and
isolated thunderstorms are elsewhere north of 15N and west of 81W.

Tropical Storm Isaac near 14.6N 49.7W 996 mb at 11 AM EDT moving
W at 14 kt. Maximum sustained winds 60 kt gusts 75 kt. Isaac will
move to 14.6N 51.8W this evening, strengthen to a hurricane near
14.7N 54.4W Wed morning, then weaken to a tropical storm near
14.9N 57.1W Wed evening, reach to near 15.1N 59.9W Thu morning and
to 15.5N 65.5W Fri morning. Isaac will change little in intensity
as it moves to near 15.5N 71.0W early Sat. Expect winds and seas
to increase over the far eastern Caribbean beginning late Wed into
Thu.

ATLANTIC OCEAN...

Please refer to the Special Features section above for details
on Hurricanes Florence and Helene and on Tropical Storm Isaac.

An upper-level trough extends from a nearly stationary upper-
level low near 31N34W southwestward to 26N40W, where it becomes a
cyclonic shear axis to a small upper-level low dropping south at
24N48W and to near 23N55W. Upper-level cyclonic flow covers the
area generally to the north of 23N between 26W and 54W. Scattered
showers and isolated thunderstorms are within 120 nm in the NE and
90 nm in the SW semicircles of the low near 24N48W, and also north
of 30N from 34W to 38W. Isolated showers and thunderstorms are
elsewhere west of 40W, except for scattered showers and isolated
thunderstorms north of 26N west of 74W enhanced by the combiation
of an inverted surface trough that is offshore the coast of
Florida from 26N79W to 31N81W, and an upper trough axis that
extends into the far northwest corner of the area from 32N79W to
northeastern Florida.

Hurricane Florence near 26.7N 65.3W 950 mb at 11 AM EDT moving
WNW at 14 kt. Maximum sustained winds 115 kt gusts 140 kt.
Florence will move to 27.7N 67.6W this evening, 29.4N 70.6W Wed
morning, 31.1N 73.1W Wed evening, and will move to a position
north of the area near 32.6N 75.2W Thu morning.

For additional information please visit
http://www.hurricanes.gov/marine

$$
Aguirre
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