Tropical Discussion

285

axnt20 knhc 111731

twdat

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 analysis...weather

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.

...ITCZ...

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.

...Discussion...

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.

$$

Walton