[Tropical] Tropical Weather Discussion

[EMWIN Server]

AXNT20 KNHC 182332
TWDAT

TROPICAL WEATHER DISCUSSION
NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL
805 PM EDT THU AUG 18 2005

TROPICAL WEATHER DISCUSSION FOR NORTH AMERICA...CENTRAL
AMERICA... GULF OF MEXICO...CARIBBEAN SEA...NORTHEASTERN
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
2315 UTC.

...TROPICAL WAVES...

E ATLC TROPICAL WAVE REPOSITIONED ALONG 27/28W S OF 20N MOVING W
10-15 KT.  LONG-TERM SATELLITE LOOPS SUGGEST THAT THE WAVE HAS
BEEN SLOWLY MOVING WESTWARD WITH A SPOKE OF ENERGY BROKEN OFF
FROM THE WAVE NEAR 21N22W.  SURFACE OBSERVATIONS FROM THE CAPE
VERDES SUGGEST PRESSURE HAVE RISEN A COUPLE OF MB SINCE
YESTERDAY... A SIGN OF WAVE PASSAGE.. IN ADDITION TO SHIP
OBSERVATIONS POINTING TO A BROAD LOW NEAR 14N27W.  THIS WAVE IS
QUITE BROAD WITH CYCLONIC LOW-LEVEL FLOW NOTED AS FAR W AS
40W.   THE WAVE COULD BEGIN MOVING A BIT FASTER NOW THAT IT IS A
LITTLE FARTHER AWAY FROM THE ENHANCING WLY WINDS NEAR W AFRICA.
ANY SIGNIFICANT CONVECTION IS WITHIN THE ITCZ.

W ATLC WAVE ALONG 55W S OF 18N MOVING W 15 KT.  ISOLATED TSTMS
ARE ALONG THE WAVE AXIS WITH MUCH DRIER AIR ASSOCIATED WITH
AFRICAN DUST SEEN IN VISIBLE IMAGES FROM THE WAVE AXIS E TO
42W.  MOISTURE FROM THIS WAVE SHOULD INCREASE RAIN CHANCES IN
THE LESSER ANTILLES OVERNIGHT INTO TOMORROW WITH PERHAPS A MUCH
DRIER WEEKEND.

W CARIBBEAN WAVE IS ALONG 82W S OF 20N MOVING W 10 KT.  A BROAD
MID-LEVEL ROTATION IS SEEN IN VISIBLE SATELLITE WITH A LEFTOVER
MCV NEAR 1382W FROM DYING CONVECTION.  A LARGE AREA OF DISTURBED
WEATHER PERSISTS NEAR AND E OF THE WAVE AXIS WITH PERHAPS
ANOTHER TROPICAL WAVE ALONG 72W RESPONSIBLE FOR THE CONVECTION
THERE.  WIDELY SCATTERED SHOWERS AND ISOLATED TSTMS ARE FROM
11N-18N BETWEEN 78W-84W.

SW GULF WAVE IS ALONG 95W/96W S OF 22N MOVING W 10-15 KT.  A FEW
TSTMS ARE NEAR 19N95W ASSOCIATED WITH THE WAVE... WHICH COULD
ENHANCE RAIN CHANCES IN SE MEXICO TOMORROW AS IT MOVES IN.

...ITCZ...

ITCZ AXIS IS ALONG 16N18W 8N38W 11N53W.  SCATTERED MODERATE
WITHIN 30 NM OF LINE 9N29.5W 8N34W.  ISOLATED MODERATE FROM
6N-12N BETWEEN 23W-30W AND WITHIN 45 NM OF AXIS BETWEEN
35W-42W.

...DISCUSSION...

GULF OF MEXICO...
MID/UPPER LOW NEAR 27N95W IS CAUSING THE MOST WEATHER WITH A
LARGE AREA OF ISOLATED TSTMS N OF 23 W OF 90W ENHANCED BY THE
LOW.  OTHERWISE A LARGE UPPER HIGH SITS NEAR GEORGIA WITH DEEP
ELY FLOW S OF A RIDGE AXIS ALONG 28N.  FAIRLY DRY AIR ALOFT IS
KEEPING THE TYPICAL FLORIDA TSTMS RATHER SPARSE AND THE ELY
WINDS ARE CAUSING THE TSTMS TO PREFERENTIALLY FORM ON THE W
COAST.  THE UPPER LOW IS EXPECTED TO MOVE INLAND TOMORROW WITH
THE UPPER HIGH BASICALLY CONTROLLING THE REGION.  THE BEST
CHANCES OF RAIN SHOULD BE ALONG THE TEXAS COAST AND SW GULF OF
MEXICO WHERE MOISTURE FROM TROPICAL WAVES SHOULD KEEP THINGS
UNSETTLED.

CARIBBEAN SEA...
BROKEN UPPER TROUGH LIES FROM NE NICARAGUA TO HAITI WITH A LOW
CENTER NEAR 14N84W IN NE NICARAGUA AND ANOTHER CLOSE TO HAITI.
UPPER DIVERGENCE COMBINED WITH TROPICAL WAVES AND COPIOUS
MOISTURE IS LEADING TO A VERY WET DAY IN THE CENTRAL CARIBBEAN.
WIDELY SCATTERED SHOWERS AND A FEW TSTMS COVER THE AREA N OF 15N
BETWEEN 67W-77W.  UPPER RIDGING IS TRYING TO BUILD OVER THE
SOUTHERN CARIBBEAN WITH A HIGH NOTED NEAR 13N81W AND A RIDGE
AXIS S OF 18N ALONG 70W.  THE AREA OF WET WEATHER SHOULD SHIFT
SLOWLY WESTWARD IN TANDEM WITH THE UPPER TROUGH... OVERSPREADING
THE REST OF THE NW CARIBBEAN BY EARLY SAT.  COMPUTER MODELS
CONTINUE TO SUGGEST THAT A BROAD LOW IN THE SW CARIBBEAN IN THE
MIDDLE LEVELS COULD MOVE NORTHWARD AND INTERACT WITH A SURGE IN
MOISTURE ALONG 72W... POSSIBLY LEADING TO AN ENHANCED CHANCE OF
TROPICAL GENESIS IN THE W CARIBBEAN.  UPPER WINDS SHOULD BECOME
A LITTLE MORE FAVORABLE FOR DEVELOPMENT DURING THE NEXT 48 HOURS
AND IT IS AN AREA TO BE WATCHED AT THE LEAST.

ATLANTIC OCEAN...
AN UPPER HIGH CENTERED OVER THE SE USA CONTROLS THE WEATHER W OF
75W.. GENERALLY DRIER THAN AVERAGE.  HOWEVER AN INVERTED TROUGH
EXTENDS FROM HAITI TO 30N65W WITH INSTABILITY ALOFT COUPLED WITH
UPPER DIVERGENCE SPREADING A LARGE AREA OF WIDELY SCATTERED
SHOWERS AND TSTMS S OF 25N BETWEEN 66W-73W.  THIS RAIN AREA
SHOULD SLOWLY PROGRESS WESTWARD... INTO THE CENTRAL BAHAMAS BY
LATE TOMORROW.   UPPER RIDGING IS BEHIND THE TROUGH... CENTERED
NEAR 28N55W WITH A HIGH.  A WEAK SURFACE TROUGH COMBINED WITH
THE HIGH IS LEADING TO WIDELY SCATTERED MODERATE CONVECTION
WITHIN 60 NM OF LINE 29N53W 28N59W.  FARTHER E... THE NEWEST
UPPER LOW TO ENTER THE AREA IS NEAR 29N42W DROPPING SOUTHWARD
WITH TROUGH AXIS TO 20N45W.  THIS LOW IS FORECAST BY THE GFS TO
CONTINUE MOVING SOUTHWARD BUT NOT MOVE AS FAR SOUTH AS THE LAST
TROUGH.. THE ONE THAT KILLED TD 10.  OTHERWISE IN THE AREA...
MID/UPPER LOW IS W OF MADRAS ISLAND NEAR 32N20W WITH PLENTY OF
DEEP MOISTURE IN AREAS THAT ARE FAIRLY DRY ON AVERAGE.  UPPER
RIDGING HAS BUILT IN FOR THE TIME BEING ACROSS THE DEEP
TROPICS... WITH RIDGE AXIS ROUGHLY FROM 21N17W 20N59W...
SLIGHTLY BROKEN FROM A TROUGH ALONG 45W.  DIVERGENT ELY FLOW IS
ENHANCING ITCZ CONVECTION THOUGH FARTHER N ... WATER VAPOR
IMAGES INDICATE THERE IS SUBSTANTIAL SUBSIDENCE ALOFT.  THIS
APPEARS TO BE DUE TO CONVERGENCE BETWEEN AN UPPER TROUGH ALOFT
45W AND THE UPPER RIDGE IN THE DEEP TROPICS.  A LARGE AREA OF
TSTMS IS ALONG 10W... PROBABLY THE NEXT TROPICAL WAVE TO ENTER
THE AREA.  IT MIGHT BE WORTH A SMALL MENTION THAT THERE IS
UNANIMOUS AGREEMENT AMONG THE MODELS OF SOME SORT OF ATTEMPTED
TROPICAL CYCLONE FROM THE WAVE AFTER IT LEAVES THE COAST IN A
COUPLE OF DAYS.   AT THE SURFACE... 1025 MB HIGH LIES NEAR
37N35W RIDGING TO 30N43W THEN SW TO 25N60W.  TRADES ARE BELOW
AVERAGE IN THE DEEP TROPICS.

$$
BLAKE


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