Tropical Discussion

Posted September 11, 2009

axnt20 knhc 111731

Tropical weather discussion
NWS TPC/National Hurricane Center Miami FL
205 PM EDT Fri Sep 11 2009

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...meteorological
observations...and radar.

Based on 1200 UTC surface analysis and satellite imagery through
1645 UTC.

...Special features...

Hurricane Fred is centered near 18.0n 35.0w at 11/1500 UTC or
about 640 nm WNW of the Cape Verde Islands drifting to the N at
1 kt. Little motion is expected over the couple of days.
Estimated minimum central pressure is 983 mb. Maximum sustained
winds have decreased to 70 kt with gusts to 85 kt. Further
weakening of Fred is expected. Scattered moderate/strong
convection is from 17n-20n between 31w-36w. Scattered showers
remain farther N from 20n-27n between 26w-35w.See latest NHC
forecast/ advisory under AWIPS/WMO headers miatcmat2/wtnt22 knhc
for more details.

...Tropical waves...

Tropical wave is along 20w S of 19n moving W near 15 kt. A 1010
mb low is along the wave axis near 12n. Visible satellite
imagery and an earlier Quikscat pass confirmed the location of
the low circulation. Scattered moderate/isolated strong
convection is from 13n-17n between 20w-22w.

Tropical wave is along 80w S of 19n moving W near 18 kt. The
wave follows a maximum in deep layer moisture observed in total
precipitable water imagery. The wave has moved under moist sly
flow aloft around an upper level low over Nicaragua which has
enhanced a large cluster of numerous strong convection from
11n-16n between 81w-85w. The convection may be more associated
with upper level diffluent flow than surface convergence near
the wave.


The ITCZ axis is centered along 9n12w 8n23w 13n30w 12n40w 10n53w
9n63w. Scattered moderate convection is from 5n-10n between
20w-28w. Isolated moderate convection is within 50 nm either
side of the axis between 37w-46w.


Gulf of Mexico...
as of 1500 UTC...a 1012 mb surface low is analyzed off the Texas
coast near 27n96w. A surface trough extends through the low
center from the Louisiana coast near 30n92w to the low center
continuing to 24n98w. This system is supported by an upper level
trough forming over Mexico and Texas extending into the far W
Caribbean. Surface convergence near the surface low and trough
along with upper level diffluence between the upper trough and
an upper level ridge dominating the central Gulf are supporting
scattered showers/thunderstorms across much of the Gulf from
25n-30n W of 84w...and S of 25n W of 92w. A second surface
trough is analyzed from Fort Myers Florida near 27n82w to the
central Gulf near 26n91w continuing SW to the Bay of Campeche
near 20n95w. Surface convergence near this trough is enhancing
the aforementioned shower activity associated with the surface
low and trough in the NW Gulf a well as an area of scattered
showers/thunderstorms along the W Florida coast from 23n-27n E
of 83w. Expect showers/thunderstorms to continue as the trough
in the se and central Gulf moves NW and joins the trough in the
NW Gulf.

Caribbean Sea...
an upper level low is centered over Nicaragua near 12n84w
covering the SW Caribbean with troughing extending to the NE
across the central Gulf connecting to another upper level low N
of Puerto Rico. Upper level diffluence along the E side of the
base of the upper trough is enhancing a large cluster of
numerous showers/thunderstorms from 11n-16n between 81w-85w.
This activity is also influenced by surface convergence near a
tropical wave along 80w. Upper level ridging is across the NW
Caribbean continuing from the central Gulf. Upper diffluent flow
between this ridge and an upper level trough across the Bahamas
is supporting a few isolated showers/thunderstorms just S of
Cuba. The remainder of the central and E Caribbean is under
moderately dry air and zonal wly flow aloft. Moderate to fresh
trade winds are across much of the basin with stronger winds
near the coast of Colombia and in the E Caribbean. Expect the
wave along 80w to continue wwd and move across Central America.

Atlantic Ocean...
as of 1500 UTC...a surface trough enters the discussion area
near 32n74w continuing along 29n78w to the Florida coast near
28n80w and into the Gulf of Mexico. The trough is supported by
an upper level trough extending along 76w to the Bahamas.
Surface convergence near the trough along with upper level
diffluence between the upper trough and an upper level ridge to
the E of the trough with axis along 32n64w to 22n72w are
supporting a wide area of isolated showers/thunderstorms within
400 nm se of the trough axis. A weak surface ridge is to the E
of the surface trough anchored by a 1021 mb high near 29n61w. A
cold front dips into the area E of the surface high extending
along 32n43w 30n51w 31n55w continuing as a stationary front NW
out of the discussion area. A pre-frontal trough is analyzed
ahead of the front from 31n42w to 29n49w. Scattered
showers/thunderstorms are within 150 nm ahead of the front. A
few isolated showers are N of Puerto Rico from 19n-24n between
64w-69w in association with an upper level low near 24n65w. A
surface trough is analyzed from 21n48w to 14n50w supported by an
upper level trough extending along 32n27w 26n38w 21n49w. An
upper level ridge dominates the E and tropical Atlc centered
just off the coast of Africa near 19n20w enhancing convection
along the ITCZ and sheering the convection near Hurricane Fred.



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