[Tropical] Tropical Weather Discussion

[EMWIN Server]

AXNT20 KNHC 061718
TWDAT

Tropical Weather Discussion
NWS National Hurricane Center Miami FL
1805 UTC Mon Sep 6 2021

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 31N. The following information is based on satellite
imagery, weather observations, radar and meteorological analysis.

Based on 1200 UTC surface analysis and satellite imagery through
1700 UTC.

...SPECIAL FEATURES...

Hurricane Larry is centered near 22.1N 52.9W at 1500 UTC, moving
NW at 9 kt. Estimated minimum central pressure remains 956 mb.
Maximum sustained wind speed is 105 kt with gusts to 130 kt. The
large eye diameter is 60 nm on IR satellite imagery. Numerous
moderate to strong convection is noted within 150 nm SW and 120 nm
NE semicircles. Seas of 12 ft or higher extend outward 300 to 330 nm
from the center in the N semicircle, and 270 nm across the S
semicircle, with maximum seas estimated at 46 ft. On the forecast
track, a northwest motion with a slight decrease in forward speed
is expected during the next few days, passing east of Bermuda.
Minor fluctuations in strength are forecast during the next day
or so, followed by very gradual weakening. Swells generated by
Larry are reaching the Lesser Antilles and are expected to spread
westward to portions of the Greater Antilles, the Bahamas, and
Bermuda later today and Tuesday. Significant swells should reach
the east coast of the United States and Atlantic Canada by
midweek. These swells are expected to cause large and dangerous
surf which will produce life-threatening rip currents. Please read
the latest High Seas Forecast issued by the National Hurricane
Center at website https://www.nhc.noaa.gov/text/MIAHSFAT2.shtml
and the latest NHC Forecast/Advisory and Public Advisory at
www.hurricanes.gov for more details.

...TROPICAL WAVES...

An eastern Atlantic Ocean tropical wave has an axis along 26W-27W,
from 19N southward, moving W around 15 kt. A 1013 mb low along the
wave was depicted near 11N27W by a recent ASCAT pass, and also
showed evidence of the wave at the surface. Scattered moderate
isolated strong convection is noted along the trough from 05N to
10N between 21W and 33W. Scattered moderate convection is noted NW
of the low from 12N to 15.5N between 26.5W and 29W.

A central Atlantic Ocean tropical wave has an axis along 45W,
from 17N southward, moving W at 10 to 15 kt. The wave is situated
at the leading edge of a Saharan dust plume, so no significant
convection is associated with this wave. Recent ASCAT data showed
NE winds of 15 to 20 kt at the surface immediately behind the
wave.

A Caribbean Sea tropical wave has an axis along 82W, south of 18N
through western Panama, moving W at 10 kt. Scattered moderate to
strong convection extends from the eastern Pacific Ocean near 06N
to 16N in the Caribbean between 74W and 83.5W. Recent ASCAT data
shows an easterly wind surge of 15 to 20 kt behind this wave,
which is aiding in forcing convection there.

...MONSOON TROUGH/ITCZ...

The monsoon trough extends into the Atlantic Ocean off the coast
of Africa, along the border of Mauritania and Senegal near 16.5N
16.5W, to low pressure along a tropical wave near 11N27W to 06.5N34.5W.
The ITCZ extends from 06.5N35W to 04N47W to 04.5N54W. Aside from
the convection mentioned in the Tropical Waves section above,
scattered moderate isolated strong convection is noted from 04N
to 07N between 35W and 44W and from 05N to 09.5N between 48W and
54W.

GULF OF MEXICO...

A weak 1017 mb high is centered across the extreme SE Gulf and
adjacent SW Florida coast. A surface trough extends across the
eastern Bay of Campeche to near 23N92W, while a stalling frontal
boundary is along the SW Louisiana coast extending NE across south
Mississippi. The modest pressure gradient between these features
is producing gentle to moderate S to SW winds across the S central
and east portions of the Gulf, around the periphery of the high. A
middle to upper level cyclone is cut off across the central Gulf
along about 90W and is promoting scattered showers and
thunderstorms across central portions from 22N to 27N between 84W
and 90W, and to the east of the surface trough, between it and the
W coast of the Yucatan Peninsula.

The surface trough off the NW coast of the Yucatan Peninsula is
forecast to move N or NE over the central and NE Gulf of Mexico
over next few days, likely reaching the northern Gulf coast by
mid-week. Upper-level winds are currently unfavorable for tropical
development, but could become somewhat conducive for formation
before it reaches the coast. Aside from this low pressure, high
pressure will bring light to gentle winds and slight seas into
mid-week.

CARIBBEAN SEA...

See the Tropical Waves section above for details on the tropical
wave moving into the western Caribbean.

A very modest pressure gradient across the basin between high
pressure south of Bermuda and low pressure along the monsoon
trough exiting NW Colombia is yielding moderate to fresh trade
winds across the basin between 65W and 80W, where seas are
generally 4 to 7 ft. Swell from distance hurricane Larry is beginning
to enter Atlantic passages off the Leeward Islands, where seas of
5 to 7 ft are occurring. Buoy 42060 located WSW of Montserrat is
currently reporting E swell of 3 ft at 13 seconds.

An upper level trough extends from the Atlantic north of Puerto
Rico southwestward across Hispaniola to offshore of Honduras and
Nicaragua. This upper level pattern is supporting the convection
described with and behind the tropical wave along 82W. Moderate NE
winds are converging across the Leeward Islands and the adjacent
NE Caribbean where small clusters of moderate thunderstorms are
occurring.

Major Hurricane Larry will remain well to the northeast of the
Leeward Islands today and tonight and continue moving
northwestward and farther north of the area through mid week.
Associated moderate to large swell will continue to spread west
and southwestward across the Leeward Islands and Atlantic passages
into mid week. Elsewhere, gentle to moderate trade winds will
persist, pulsing to fresh winds off Colombia mainly at night.

ATLANTIC OCEAN...

Please see the Special Features section for details on Category 3
Hurricane Larry.

A middle to upper level cyclone is located west of Larry, is centered
near 22.5N 66W and nearly stationary. A small middle to upper
level cyclone can be seen in satellite imagery moving slowly NE
and off the central coast of Florida. Associated upper level
divergence associated with both of these features is supporting
active scattered convection from 25N to 30N between 65W and 72W,
where moderate SW to W winds are converging at the surface south
of a weak trough. Small scattered clusters of moderate convection
are also across the NW Bahamas and extend N to offshore of Florida
to 29N.

At the surface, weak high pressure is drapped across the north of
Larry, with weak high centers of 1018 mb near 25N64W and another
1018 mb high near 25N41W. Thus, generally outside of Larry, light
to gentle wind prevails with seas of 3 to 7 ft west of 66W. Buoy
43043 located NNE of San Juan, Puerto Rico is reporting eastern
swell approaching 8 ft at 15 seconds. Smaller east swell of this
wave length will reach the SE Bahamas and adjacent waters to the
north this afternoon.

To the S and E of Larry, generally S of 20N and E of 50W,
moderate to fresh NE trades prevail. A weakening cold front is
noted in the northeast basin, from 30N18W to 27N27W to 30N37W. No
convection is associated with this front, and winds north of the
boundary are N and gentle to moderate.

Major Hurricane Larry will move to 23.1N 54.0W this evening,
24.5N 55.3W Tue morning, 25.9N 56.6W Tue evening, 27.5N 58.0W Wed
morning, 29.3N 59.6W Wed evening. Larry will move north of the
area near 31.6N 61.2W Thu morning. Large swell generated by Larry
will continue to propagate westward across waters north through
northeast of the Leeward Islands and spread west of 68W this
afternoon, reaching 72W by mid week.

$$
Stripling
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