[Tropical] Tropical Weather Discussion

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AXNT20 KNHC 070050 AAA
TWDAT

Tropical Weather Discussion...Updated
NWS National Hurricane Center Miami FL
850 PM EDT Thu Sep 6 2018

Updated Atlantic Ocean section for convection coverage

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
0000 UTC.

...SPECIAL FEATURES...

Hurricane Florence is centered near 25.0N 49.6W at 06/2100 UTC,
which is about 900 nm east-northeast of the northern Leeward
Islands or 915 nm east-southeast of Bermuda. It is moving NW or
305 degrees at 9 kt. The estimated minimum central pressure is
989 mb. Maximum sustained winds have diminished to 70 kt with
gusts to 85 kt. Latest satellite imagery shows that the cyclone
has been undergoing southwesterly vertical upper-level shear as
noted by its rather tilted NE to SW cloud/convection structure in
its northeastern quadrant. The imagery also shows what appears
to be the low-level center exposed on the southwest side of the
cyclone's deep convection. The deep convection consists of the
scattered moderate isolated strong type intensity from 25N to
27N between 45W and 48W. Similar convection is within 60 nm NE
of the center. The latest NHC forecast calls for Florence to
move northwestward through tonight before it turns toward to the
west on Fri. It is forecast to weaken slightly through Fri, then
strengthen late on Fri. See latest NHC forecast/advisory under
AWIPS/WMO headers MIATCPAT1/WTNT31 KNHC for more details.

A broad and elongated area of low pressure is centered several
hundred miles west-southwest of the Cabo Verde Islands is denoted
by a tropical wave with its axis along 32W/33W and extending from
04N to 20N. A 1008 mb low is on the wave axis near 14N32W. This
system is moving westward at 10 to 15 kt. The associated shower
and thunderstorm activity has not yet increased in organization.
Latest satellite imagery shows scattered moderate isolated strong
convection within 210 nm of the low in the NE quadrant, and
within of the low in the W quadrant. Scattered moderate convection
is within 30 nm of 15N33W. Environmental conditions are conducive
for development, and a tropical depression is expected to form
within the next day or two while the system moves slowly westward
or west-northwestward across the tropical Atlantic. The chance of
this system becoming a tropical cyclone during the next 48 hours
remains high. Please read the latest NHC Tropical Weather Outlook
under AWIPS/WMO headers MIATWOAT/ABNT20 KNHC for more information.

A tropical wave just inland along the coast of western Africa has
its axis near 15W from 04N to 20N, with a 1008 mb low on the axis
at 14N15W. This system is moving westward at 10 to 15 kt. Latest
satellite long term animation indicates that this system is
exhibiting signs of organization. Large clusters of scattered
moderate to strong convection are observed in advance of this
system from the coastal sections of Senegal to Sierra Leone, west
to 18W and eastward to within 240 nm inland the coast of Africa.
A tropical depression is likely to form over the weekend or early
next week while the wave and associated low pressure moves
westward or west-northwestward over the far eastern tropical
Atlantic Ocean. The chance of this system becoming a tropical cyclone
during the next 48 hours is in the medium range. Interests in the
Cabo Verde Islands should monitor the progress of this system.
Please read the latest NHC Tropical Weather Outlook under
AWIPS/WMO headers MIATWOAT/ABNT20 KNHC for more information.

...TROPICAL WAVES...

A tropical wave has its axis along 80W south of 20N, moving
westward at 10 to 15 kt. Scattered moderate convection is
within 120 nm east of the wave from 13N to 15N, and from 18N to
20N within 120 nm east of the wave. Scattered showers and
isolated thunderstorms are elsewhere within 120 nm either side
of the wave.

A tropical wave has its axis along 94W and south of 21N, and
continues southward across southeastern Mexico and the Isthmus of
Tehuantepec and further southward to the eastern Pacific near
04N. It is moving westward near 15 kt. Only isolated showers are
seen within 60 nm of the wave axis.

...MONSOON TROUGH/ITCZ...

The monsoon trough axis extends from the coastal sections of
Senegal near 14N17W, to the 1008 mb low that is associated with
the tropical wave along 32W/33W as discussed in the Special
Features section. It continues from this low to 10N37W to 08N41W.
The ITCZ extends from 08N41W to 08N50W to 08N59W. Aside from the
convection described above associated with the two tropical waves
along 32W/33W and the one inland the coast of Africa near 15W,
only scattered moderate convection is seen within 60 nm south of
the ITCZ between 46W and 54W.

...DISCUSSION...

GULF OF MEXICO...

Upper-level cyclonic flow is located over eastern Louisiana and
Mississippi while upper-level anticyclonic flow is located over
the west-central Gulf of Mexico. A moist and unstable atmosphere
continues to support scattered moderate convection over the
far NW Gulf northwest of a line from just west of Mobile to
28N91W to Brownsville. Scattered moderate convection has moved
offshore the west Florida coast to the extreme eastern gulf
waters from 24N to 29N east of 85W. Isolated showers and
thunderstorms are elsewhere across the Gulf.

A weak surface ridge will build from the Carolinas to the coast
of Texas in the wake of Gordon. Over the southeastern two-thirds
of the Gulf of Mexico, gentle easterly winds will prevail through
Fri. Thereafter, expect gentle to moderate easterly winds and
modest seas into early next week. The exception will be fresh
winds pulsing off the west coast of the Yucatan Peninsula, mainly
during the late evening hours, due to a daily trough that sets up
in the far southwestern Gulf of Mexico.

CARIBBEAN SEA...

Please see Tropical Waves section above for details regarding
a tropical wave along 80W.

Upper-level cyclonic flow covers the western Caribbean Sea west
of a Hispaniola to Panama line, while upper level anticyclonic
flow covers the eastern Caribbean. Aside from convection
related to the tropical wave, isolated showers and thunderstorms
are elsewhere west of 74W.

A relatively weak surface ridge in the western Atlantic Ocean
will maintain moderate to fresh trade winds in most of the region
through late Sun.

ATLANTIC OCEAN...Updated

Please read the Special Features section above for details about
Hurricane Florence. Two areas of tropical development interest
pertains to a broad area of low pressure in the eastern Atlantic
near 14N32W, with a high chance of development and a vigorous
tropical wave and low pressure system nearing the coast of
Africa, with a medium chance of development.

A large upper-level low located over the Bahamas and Cuba is
moving west-northwestward. Associated upper level cyclonic flow
covers the Atlantic west of 67W from the Greater Antilles to 34N.
A westward moving surface trough is analyzed from 31N75W to
the NW Bahamas and to 23N80W. Another surface trough is analyzed
from near 32N67W to 26N65W. Scattered to numerous moderate
convection cover just about the entire western half of the basin
north of 21N west of 70W, and also north of 28N between 50W and
70W.

A weak pressure pattern will maintain gentle to moderate easterly
winds across the western Atlantic area through Sun night.
Easterly swell from Hurricane Florence will move into the open
waters east of the Bahamas starting this weekend.

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

$$
Aguirre
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