[Tropical] Tropical Weather Discussion

[EMWIN Server]

AXNT20 KNHC 160605
TWDAT

Tropical Weather Discussion
NWS National Hurricane Center Miami FL
205 AM EDT Sun Sep 16 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 0000 UTC surface analysis and satellite imagery through
0545 UTC.

...SPECIAL FEATURES...

Tropical Storm Florence is centered near 33.7N 80.8W at 16/0600
UTC, or about 20 nm SE of Colombia South Carolina moving W at 5
kt. Estimated minimum central pressure is 999 mb. Maximum
sustained wind speed is 35 kt with gusts to 45 kt. Satellite
imagery shows that the cyclone has lost just about of its deep
convection over the SW semicircle, where only areas of rain with
scattered showers and isolated thunderstorms are observed.
Scattered moderate isolated strong convection is between 90 and
240 nm of the center over the NE and E quadrants. The latest NHC
advisory has Florence turning toward the northwest, with an
increase in forward speed today, followed by a turn toward the
north and northeast with an additional increase in forward speed
on Mon. On this forecast track, Florence's center will move across
the western Carolinas on Sun and then recurve over the Ohio
Valley and northeastern U.S. Mon and Tue. See the latest NHC
forecast/advisory under AWIPS/WMO headers MIATCPAT1/WTNT31 KNHC
for more details.

Tropical Storm Helene is centered near 41.2N 30.41 at 16/0300
UTC, or 170 nm NNW of Faial Island In The Central Azores moving NE
at 22 kt. Estimated minimum central pressure is 989 mb. Maximum
sustained wind speed is 50 kt with gusts to 69 kt. Helen continues
to be hampered by vertical shear and cold sea surface
temperatures. The center of Helene is observed on satellite
imagery to be the west of the its related deep convective
activity. This activity consists of the scattered moderate
isolated strong type intensity from 40N to 43N between 25W and
30W. Scattered showers and isolated thunderstorms are from 38N to
40N between 23W and 28W. Helene is forecast to continue on its
present motion, with an increase in forward speed expected during
the next couple of days. On the current forecast track, Helene
should move away from the Azores overnight and then approach
Ireland and the United Kingdom tonight and Mon. See the latest NHC
forecast/advisory under AWIPS/WMO headers MIATCPAT3/WTNT33 KNHC
for more details.

Tropical Storm Joyce is centered near 33.4N 38.0W at 16/0300 UTC
or 600 nm WSW of the Azores moving E at 15 kt. Estimated minimum
central pressure is 1003 mb. Maximum sustained wind speed has
decreased to 35 kt with gusts to 45 kt. Latest satellite imagery
shows that the cyclone is exhibiting a highly sheared pattern
type, with its low-level center well remove from its related
convection. The convection consists of the scattered moderate
type intensity to the northeast of the center from 35N to 37N
between 34W and 38W. Joyce is forecast by the latest NHC advisory
to continue on its current motion over the next day or so, with a
decrease in forward speed. After that time, Joyce should turn
east-southeast away from the Azores. See the latest NHC
forecast/advisory under AWIPS/WMO headers MIATCPAT5/WTNT35 KNHC
for more details.

...TROPICAL WAVES...

A far eastern Atlantic tropical wave has its axis extending from
near 05N33.5W to 13N35W and to near 20N35W, moving westward at
10-15 kt. The wave is supported by broad troughing at the 700 mb
level, but is surrounded by a rather dry environment from dust
that moved off the coast of Africa a few days ago, and is
spreading westward across the eastern Atlantic. These dry
conditions are inhibiting convection from developing along or
near the wave. Only scattered showers and thunderstorms are within
150 nm east and 120 nm w of the wave axis from 06N to 08N.

...MONSOON TROUGH/ITCZ...

The monsoon trough axis extends from well inland Africa southwestward
to the coast of Guinea-Bissau and continues to 09N10W and to
08N26W. The ITCZ extends from 08N26W to just east of the above
described tropical wave, and resumes just west of the same
tropical wave to 09N43W to 09N53W. Aside from the shower and
thunderstorm activity associated with the above described tropical
wave, scattered moderate convection is within 120 nm south and 90
nm north of the ITCZ between 43W and 53W. Similar activity is
south of the ITCZ within 30 nm of a line from 07N36W to 07N43W.
Other scattered moderate convection is to the northwest of the
ITCZ within from 09N to 11N between 53W and 55W.

...DISCUSSION...

GULF OF MEXICO...

An upper-level low located north of the Yucatan Peninsula near
23N89W is moving westward. A trough extends from the low to
inland the central Yucatan Peninsula. Its cyclonic flow covers the
central gulf section. Upper-level high pressure ridging stretches
from Oklahoma southward to eastern Texas and eastern Mexico north
of 22N. Northerly flow produced by the anticyclonic flow over the
ridge is channeling broken to overcast mid and high level clouds
southward across much of the western gulf west of 92W. Isolated
showers and thunderstorms are possible underneath these clouds.
Areas of light to moderate rain along with scattered to numerous
showers and thunderstorms over deep southern Texas associated with
a surface trough and attendant weak low pressure that are slowly
moving westward.

CARIBBEAN SEA...

A 1006 mb small low analyzed over the central Caribbean near
16N72W has a trough extending north-northeast to the border of
Haiti and the Dominican Republic and south to near 13N72W. This
system depicts is associated with the remnants of recent tropical
cyclone Isaac. Scattered moderate isolated strong convection
is seen within 30 nm either side of a line from 15N72W to 15N73W.
Scattered moderate convection is within 30 nm either side of a
line from 15N71W to 17N71W. This area of low pressure is forecast
to bring locally heavy rains and gusty winds across portions of
Hispaniola, Jamaica, and eastern Cuba during the next couple of
days, with the possibility of it undergoing some slow development.
The Ascat pass from Sat shows mainly moderate to fresh winds with
the low, with a few winds of strong intensity within the
aforementioned convection. Gentle trades are west of the low and
trough, while gentle to moderate trades are elsewhere east of the
low and trough. A far eastern tropical wave will move across
the tropical waters east of the windwards on Tue accompanied by
fresh to locally strong trades and building seas.

The southern tail-end of a broad central Atlantic trough extends
southwestward to the eastern Caribbean from just east of Puerto
Rico to near 16N66W. Trough energy is helping to trigger off
scattered moderate convection from 15N to 17N between 65W and 68W.
Scattered showers and isolated thunderstorms are elsewhere north
of 15N and east of 70W.

Over the far southwestern Caribbean, the eastern extent of the
eastern Pacific monsoon trough is bringing scattered showers and
thunderstorms over the water south of 12N from northwestern
Colombia westward to 76W.

ATLANTIC OCEAN...

Please refer to the Special Features section above, for details
on Tropical Storms Florence, Helene, and Joyce.

A broad deep layer trough extends across the central Atlantic
from a large and elongated upper-level low that is north of the
area near 36N52W southwestward to 32N58W to 25N64W, to just east
of Puerto and the far northeast Caribbean Sea. Plenty of
instability exists with this trough as it acts on a very moist and
unstable atmosphere. The trough is forecast to move westward
during the next few days. with an upper-level low forecast to
evolve from this trough near 28N65W by Wed.

At the surface, a 1011 mb low is near 29N64W, with a trough to
31N61W and another tough to 25N65W. A weak 1013 mb low is near
24N57W, with a trough east to southeastward to 23N51W and another
tough from the low to near 20N60W. Increasing scattered moderate
convection quickly moving south- outheastward is seen from 22N to
26N between 60W and 65W, and from 28N to 30N between 54W and 60W.
Scattered showers and isolated thunderstorms are elsewhere from
18N to 31N between 50W and 66W. Isolated showers are west of 66W,
except for scattered showers and thunderstorms that are over a
small section of the far northwestern waters of the area from 28N
to 32N between 77W and 80W due to a surface trough that extends
from just east of Tropical Storm Florence south to 32N79W, and
southwestward from there to inland northeastern Florida.

Otherwise, a rather weak pressure pattern is in place over the
central and western Atlantic, while stronger high pressure is
present over the eastern Atlantic.

An area of African dust is over the eastern Atlantic from 11N to
25N east of 37W, and is gradually migrating westward.

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

$$
Aguirre
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