[Tropical] Tropical Weather Discussion

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Sat Sep 15 00:38:00 CDT 2018


AXNT20 KNHC 150537 AAA
TWDAT

Tropical Weather Discussion...Updated
NWS National Hurricane Center Miami FL
137 AM EDT Sat Sep 15 2018

Updated Special Features section for Florence and Helene latest
information

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 1800 UTC surface analysis and satellite imagery through
0515 UTC.

...SPECIAL FEATURES...Updated

Tropical Storm Florence is centered near 33.9N 78.8W at 15/0000
UTC, or about 10 nm NNE of Myrtle Beach South Carolina moving W
at 3 kt. Estimated minimum central pressure is 975 mb. Maximum
sustained winds are 60 kt with gusts to 75 kt. Latest satellite
imagery shows that Florence is exhibiting a rather symmetrical
cloud pattern. Scattered moderate to isolated strong convection
is within 180 nm of the center in the NE quadrant and within 120
nm of the center in the SE quadrant. Scattered moderate
convection within an outer rainband is within 30 nm of a line
from 33N79W to 34N81W and to 36N81W. Latest NHC advisory has
Florence moving in a slow westward to west- southwestward
expected motion though Sat. On the forecast track, the center of
Florence will move farther inland across extreme southeastern
North Carolina this evening, and across extreme eastern South
Carolina tonight and Sat. Florence will then move generally
northward across the western Carolinas and the central
Appalachian Mountains early next week. The PUBLIC ADVISORIES for
Florence are transmitted via the WMO header WTNT31 KNHC, and via
the AWIPS header MIATCPAT1. The FORECAST/ADVISORIES for Florence
are transmitted via the WMO header WTNT21 KNHC, and via the
AWIPS header MIATCMAT1.

Tropical Storm Helene is centered near 34.9N 36.4W at 15/0000
UTC, or about 510 nm WSW of Lajes Air Base In The Azores moving
N at 16 kt. Estimated minimum central pressure is 988 mb.
Maximum sustained winds are 60 kt with gusts to 75 kt. Latest
satellite imagery shows scattered moderate convection from 35N
to 39N between 31W and 39W. Helene is forecast to move toward
the north through tonight, with a turn toward the north-
northeast expected early Sat followed by a turn toward the
northeast by Sun morning. On the forecast track, Helene will
pass near or over the Azores late Sat or Sun. The PUBLIC
ADVISORIES for Helene are transmitted via the WMO header WTNT33
KNHC, and via the AWIPS header MIATCPAT3. The
FORECAST/ADVISORIES for Helene are transmitted via the WMO
header WTNT23 KNHC, and via the AWIPS header MIATCMAT3.

Tropical Storm Joyce is centered near 31.4N 44.1W at 14/2100
UTC, or about 930 nm WSW of the Azores moving SE at 5 kt.
Estimated minimum central pressure is 1002 mb. Maximum sustained
winds are 40 kt with gusts to 50 kt. Latest satellite imagery
shows increasing convection, with a vigorous band now near the
center in the northern semicircle. The convection consists of
the scattered moderate type intensity within 180 nm of the
center in the NE quadrant, and within 90 nm of the center in the
NW quadrant. Scattered showers and thunderstorms are within 30
nm of a line from 30N47W to 30N44W to 31N42W. Joyce is forecast
by the latest NHC advisory to turn northeastward with an
increase in forward speed during the next 24 hours, followed by
an eastward turn after 48 hours. The PUBLIC ADVISORIES for Joyce
are transmitted via the WMO header WTNT3S KNHC, and via the
AWIPS header MIATCPAT5. The FORECAST/ADVISORIES for Joyce are
transmitted via the WMO header WTNT25 KNHC, and via the AWIPS
header MIATCMAT5.

Tropical Storm Isaac regained tropical storm status this
afternoon and is centered near 15.3N 68.2W at 14/2100 UTC, or
about 220 nm SSE of Santo Domingo Dominican Republic moving W at
12 kt. Estimated minimum central pressure is 1002 mb. Maximum
sustained winds are 35 kt with gusts to 45 kt. Latest satellite
imagery shows scattered moderate convection removed from the
center from 12N to 15.5N between 68W and 71W. Scattered moderate
convection is also seen to the east of Isaac from 14N to 17N
between 64W and 66W. Isaac is forecast by the Latest NHC
advisory to decrease its forward speed over the next couple of
days with a turn to the west-northwest possible by late on Sun.
On the forecast track, Isaac will move over the eastern and
central Caribbean Sea during the next few days, and be near or
south of Jamaica early next week. The PUBLIC ADVISORIES for
Isaac are transmitted via the WMO header WTNT34 KNHC, and via
the AWIPS header MIATCPAT4. The FORECAST/ADVISORIES for Isaac
are transmitted via the WMO header WTNT24 KNHC, and via the
AWIPS header MIATCMAT4.

...TROPICAL WAVES...

A far eastern Atlantic tropical wave has its axis along 30W from
08N to 21N, moving westward at 10 to 15 kt. The wave is
surrounding by a rather dry environment, which is inhibiting
deep convection from forming along or near it. Only isolated
showers and weak isolated thunderstorms are within 120 nm either
side of the wave axis where it cross the monsoon trough.

...MONSOON TROUGH/ITCZ...

The monsoon trough axis extends from near 12N16W to 09N25W to
08N32W. The ITCZ continues from 08N32W to 09N41W to 10N46W to
12N57W. Aside from the shower and thunderstorm activity
associated with the tropical wave along 30W, scattered moderate
isolated strong convection is within 180 nm south of the ITCZ from
43W to 53W. Scattered moderate convection is within 180 nm south
of the monsoon trough from 18W to 23W, and within 180 nm south of
the ITCZ between 39W and 43W.

...DISCUSSION...

GULF OF MEXICO...

An upper-level cyclonic circulation center is over north-central
gulf near 27N88W, with an inverted trough to an upper low over
the northwestern Caribbean at 20N84W that is moving westward.
Upper- level cyclonic wind flow covers the central part of the
gulf. A surface trough extends from inland central Texas to a
1009 mb low along the coast just north of Brownsville and to
24N97W to 21N97W. Scattered moderate isolated strong convection
is seen from 22N to 29N west of 92W. Isolated showers and
thunderstorms cover the rest of the gulf. Heavy rainfall and
gusty winds are likely to continue across portions of Texas and
northeastern Mexico through Sat.

A NW-to-SE orientated surface ridge will set up from central
Louisiana to Florida Bay tonight. A surface high pressure center
will develop along the ridge near 27N92W late on Saturday. The
surface high will shift slightly southward on Sunday, and the
ridge will extend southeastward to the Yucatan Basin. A weak
surface trough, extending southwestward from the remnants of
tropical cyclone Florence, will pass eastward, slowly, across
the north central Gulf waters through early next week.

CARIBBEAN SEA...

Please refer to the the Special Feature section above for
details on Tropical Depression Isaac.

An upper level cyclonic circulation center is about 100 nm to the
west of Jamaica, in the NW corner of the Caribbean Sea. Isolated
showers and thunderstorms are north of 15N and west of 80W.

Tropical Depression Isaac near 14.9N 67.3W 1007 mb at 11 AM EDT
moving W at 14 kt. Maximum sustained winds are 30 kt gusts 40 kt.
Isaac will move to 15.0N 69.0W this evening, 15.1N 71.3W Sat
morning, 15.2N 73.3W Sat evening, 15.6N 75.3W Sun morning, 17.0N
79.5W Mon morning and dissipate early Tue. The highest winds and
seas are expected mainly north of the center. Expect gentle to
moderate trade winds elsewhere, to the west of Isaac. Moderate to
locally fresh trade winds are forecast to the east of Isaac.
Strong nocturnal trade winds are forecast off the northwest coast
of Colombia on Monday night and on Tuesday night.

ATLANTIC OCEAN...

Please read the Special Features section, for details on
Tropical Storm Florence, Tropical Storm Helene, and Tropical
Storm Joyce.

An upper-level trough extends from near 32N45W to 26N48W to
20N54W, and to 16N59W. Upper level cyclonic wind flow is within
360 nm on either side of the trough. Scattered showers and
isolated thunderstorms are within 30 nm ether side of a line
from 22N44W to 22N50W to 22N57W. Isolated showers and
thunderstorms are seen elsewhere to the west of 56W.

Tropical Storm Isaac near 15.3N 68.2W 1002 mb at 5 PM EDT moving
W at 12 kt. Maximum sustained winds 35 kt gusts 45 kt.
Isaac will move to 15.4N 70.1W Sat morning, 15.4N 72.2W Sat
afternoon, 15.7N 74.2W Sun morning, weaken to a tropical
depression near 16.2N 76.3W Sun afternoon, and 17.5N 80.0W Mon
afternoon. Isaac will dissipate Tue afternoon. The highest winds
and seas are expected mainly north of the center.

A surface ridge will remain about stationary from near 32N68W to
southeastern astern  Florida through Sun. The ridge will shift
northward, to a position from 31N74W to central Florida by the
middle of the next week.

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

$$
Aguirre
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