[Tropical] Tropical Weather Discussion

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AXNT20 KNHC 111700 AAA
TWDAT

Tropical Weather Discussion...Updated
NWS National Hurricane Center Miami FL
825 AM EDT Tue Sep 11 2018

Updated Special Features section for Hurricane Florence

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
1200 UTC.

...SPECIAL FEATURES...Updated

Hurricane Florence has weakened slightly as of 8 AM this morning.
At 11/1200 UTC, Florence was centered near 26.4N 64.6W or 350 nm
S of Bermuda and about 830 nm ESE of Cape Fear North Carolina
moving WNW or 290 degrees at 13 kt. The estimated minimum
central pressure is 950 mb. The maximum sustained winds have
diminished slightly to 115 kt with gusts to 140 kt. Latest
satellite imagery shows scattered moderate to strong convection
within 150 nm of the center in the NE quadrant, and within 120
nm of the center in the SE quadrant. Scattered moderate
convection is within 150 nm of the center in the SW quadrant,
and within 180 nm of the center in the NW 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 thisforecast track, the
center of Florence will move over the southwestern Atlantic
Ocean between Bermuda and the Bahamas through Wed, 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 48.1W at 11/0900 UTC,
which is about 765 nm E of the Lesser Antilles moving W or 270
degrees at 12 kt. The estimated minimum central pressure is 997
mb. The maximum sustained wind are 60 kt with gusts to 75 kt.
Latest satellite imagery shows scattered moderate convection
within 90 nm of the center, except within 120 nm of the center
in the SE quadrant. The present motion is expected to continue
through the end of the week. On this track, Isaac should move
across the Lesser Antilles and into the eastern Caribbean Sea on
Thu. Interest in the Lesser Antilles should monitor the progress
of Isaac. 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 16.0N 33.6W at 11/0900 UTC,
which is about 540 nm west of the southernmost Cabo Verde Islands
or 1365 nm south-southwest of the Azores moving WNW or 300
degrees at 12 kt. The estimated minimum central pressure is 968
mb. The maximum sustained winds are 95 kt with gusts to 115 kt.
Latest satellite imagery shows scattered moderate convection
within 120 nm of the center in the SE and NW quadrants and
within 150 nm of the center in the NE and S quadrants and within
60 nm of the center in the SW quadrant. Helene is forecast to
maintain its present motion with a decrease in forward speed
through tonight. It is forecast to then turn toward the the
northwest and then north-northwest on Wed and Thu. 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.

...TROPICAL WAVES...

Tropical waves are not presently being analyzed.

...MONSOON TROUGH/ITCZ...

The monsoon trough is inland in Africa. The ITCZ is not analyzed
at this time. Isolated moderate to locally strong rainshowers are
elsewhere from 04N to 12N from 20W eastward, from 05N southward
between 20W and 27W, and from 10N southward between 30W and 60W.

...DISCUSSION...

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 24N88W, 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. Scattered moderate isolated strong
convection is occurring to the southeast of the upper-level low
over the southeastern gulf waters to the south of 25N east of
87W. Isolated showers and thunderstorms are elsewhere east of
91W. Please read the latest Tropical Weather Outlook under WMO
header ABNT20 KNHC, and under the AWIPS header MIATWOAT for more
details. The convection over southeastern Gulf of Mexico and the
northwestern Caribbean Sea is showing signs of organization, but
there are no signs of a surface circulation. Limited development
is anticipated today, but upper-level winds are forecast to become
more conducive, and a tropical depression could form on Thu or
Fri while the disturbance moves across the western Gulf of Mexico.
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 likely over
western Cuba and portions of the northeastern Yucatan Peninsula
today.

A stationary front is just inland the Texas coast and SW
Louisiana. 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 west of 95W. Isolated showers and 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,
through the Yucatan Channel and to a 1009 mb low over the Gulf of
Honduras at 17N87W. Latest satellite imagery shows numerous
moderate to strong convection north of 18N and west of 81W.
Scattered showers and isolated thunderstorms are elsewhere north
of 15N and west of 74W, including the Gulf of Honduras. The
numerous to strong convection is showing signs of organization,
but there are no signs of a surface circulation. Limited
development is anticipated today, but upper-level winds are
forecast to become more conducive, and a tropical depression could
form on Thu or on Fri while the disturbance moves across the
western Gulf of Mexico.

Tropical Storm Isaac near 14.6N 48.1W 997 mb at 5 AM EDT is
moving W at 12 kt, with maximum sustained winds of 60 kt gusts
to 75 kt. Isaac will move to 14.6N 50.1W this afternoon, then
become a minimal hurricane tonight near 14.6N 52.6W. Isaac will
continue to 14.8N 55.0W Wed afternoon, then weaken back to a
tropical storm near 15.1N 57.6W by late Wed night. Isaac will
continue weakening as it tracks westward to near 15.5N 62.8W
late Thu night, to near 15.6N 67.4W Fri night and to near 15.8N
72.0W Sat night. 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 an upper-level low at 30N35W
southwestward to 26N40W, where it becomes a cyclonic shear axis to
a small upper-level low dropping south at 26N48W and to near
23N55W. Upper-level cyclonic flow covers the area generally to the
north of 23N between 26W and 54W. Scattered moderate convection
is within 120 nm SE of the upper-level low at 26N48W, and within
60 nm of the upper-level low at 30N35W. Isolated showers and
thunderstorms are from 22N to 24N between 44W and 50W. Isolated
showers and thunderstorms are elsewhere west of 40W.

Hurricane Florence near 26.4N 64.16 954 mb at 8 AM EDT is moving
WNW at 13 kt, with maximum sustained winds of 115 kt with gusts
to 140 kt. Florence will move to 27.2N 66.4W this afternoon,
28.7N 69.4W tonight, 30.5N 72.2W Wed afternoon, pass to the
north of the area near 32.2N 74.5W Wed night, then approach the
Carolina coast near 34.3N 77.1W Thu night.

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

$$
Aguirre
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