[Tropical] Tropical Weather Discussion

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AXNT20 KNHC 131739
TWDAT

TROPICAL WEATHER DISCUSSION
NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL
205 PM EDT SAT AUG 13 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 1200 UTC SURFACE ANALYSIS AND SATELLITE IMAGERY THROUGH
1715 UTC.

...SPECIAL FEATURES...

THE CENTER OF TROPICAL STORM IRENE IS NEAR 30.7N 69.2W AT
13/1500 UTC OR ABOUT 440 NM SE OF CAPE HATTERAS NORTH CAROLINA
MOVING NW 9 KT. THE ESTIMATED MINIMUM CENTRAL PRESSURE IS 997 MB
AND THE MAXIMUM SUSTAINED WINDS ARE 60 KT WITH GUSTS TO 75 KT.
SEE THE LATEST NHC FORECAST/ADVISORY UNDER AWIPS/WMO HEADERS
MIATCMAT4/WTNT24 KNHC OR MIATCPAT4/ WTNT34 KNHC FOR MORE
DETAILS.  A LARGE BURST OF CONVECTION HAS DEVELOPED ON THE
SOUTHERN SIDE OF THE CENTER WITH OUTFLOW STARTING TO EXPAND
AGAIN.  RECON IS GOING AROUND THE STORM NOW AND SUGGESTS IT
COULD BE A LITTLE WEAKER WITH A SURFACE PRESSURE AROUND 1000
MB.  WATER VAPOR IMAGES SHOW A BUILDING RIDGE TO THE NORTH OF
THE CYCLONE WHICH SHOULD CAUSE A SLOWING IN THE FORWARD SPEED.
THE RIDGE IS FORECAST TO BE PROGRESSIVE SO THAT IRENE SHOULD
TURN NORTHWARD AND NE OUT TO SEA AS A MID-LATITUDE TROUGH
APPROACHES FOR EARLY NEXT WEEK.  SCATTERED MODERATE CONVECTION
WITHIN 75 NM OF THE CENTER.

1008 MB ATLANTIC LOW IS NEAR 13.5N44.5W MOVING WNW ABOUT 10 KT.
SATELLITE IMAGES INDICATE THE LOW HAS GOTTEN MUCH BETTER
ORGANIZED AND IS CLOSE TO BECOMING A TROPICAL CYCLONE.  BANDS OF
CONVECTION ARE FORMING NEAR THE CENTER AND CONVECTION HAS
SIGNIFICANTLY DEEPENING SINCE EARLY THIS MORNING.  HOWEVER ITS
DEVELOPMENT MAY BE SLOWED BY THE MID-OCEANIC TROUGH... WHICH IS
DIGGING IN ITS PATH FROM 20N46W TO 14N52W.  THIS TROUGH SHOULD
CAUSE A SLY WIND FLOW ALOFT NEAR THE LOW AND INCREASE VERTICAL
WIND SHEAR.  WIDELY SCATTERED MODERATE CONVECTION WITHIN 60 NM
OF THE CENTER WITH ISOLATED TSTMS NEAR 14N42W.

...TROPICAL WAVES...

E ATLC WAVE IS JUST W OF CAPE VERDE ISLANDS ALONG 25W/26W S OF
21N MOVING W 10-15 KT. A 1011 MB LOW PRESSURE CENTER WAS ALONG
THE WAVE FROM 15N TO 15.5N. A LARGE STRATOCUMULUS SWIRL
SURROUNDS THE LOW. NO DEEP SHOWERS AND THUNDERSTORMS ARE NEAR
THE LOW CENTER. ANY SIGNIFICANT PRECIPITATION IS IN THE ITCZ.

E CARIBBEAN WAVE IS ALONG 66W S OF 18N MOVING W 15-20 KT.  SOME
CURVATURE IS SEEN IN THE LOW CLOUDS ALONG WITH WIDELY SCATTERED
SHOWERS AND A FEW TSTMS.  THE RAIN AREA IS FROM 12.5N-18N
BETWEEN 66W-70W WITH THE BULK OF THE TSTMS WITHIN 60 NM OF
14N67.5W.  THE ENHANCED RAIN CHANCE SHOULD QUICKLY SPREAD THRU
THE CENTRAL CARIBBEAN TOMORROW...MOSTLY S OF CUBA BUT INCLUDING
JAMAICA.

CENTRAL CARIBBEAN WAVE IS ALONG 75/76W S OF 20N JUST E OF
JAMAICA MOVING W 15-20 KT.  ANY WAVE SIGNATURE IS OBSERVED BY AN
UPPER TROUGH.  HOWEVER A FEW TSTMS BETWEEN JAMAICA AND CUBA AND
WITHIN 75 NM OF 14.5N76.5W ARE PROBABLY ASSOCIATED WITH THE
WAVE.  THIS WAVE SHOULD CAUSE A INCREASE IN TSTMS OVER THE SW
CARIBBEAN ALONG WITH A BETTER CHANCE OF RAIN FOR CENTRAL AMERICA
SE OF BELIZE TOMORROW MOVING INTO YUCATAN AND THE REST OF
CENTRAL AMERICA BY MON.

WAVE ALONG PREVIOUSLY ALONG 97W/98W IS OUT OF THE AREA.

...ITCZ...

ITCZ AXIS IS ALONG 15N17W 10N31W 13N42W 10N50W 10N60W.  ISOLATED
MODERATE CONVECTION FROM 8N-11N BETWEEN 48W-52W AND WITHIN 45 NM
OF LINE 8N28W 12N42W.  WIDELY SCATTERED MODERATE WITHIN 75 NM OF
8N21W.

...DISCUSSION...

GULF OF MEXICO...
MID/UPPER LOW THAT HAS CONTROLLED THE AREA HAS BROKEN DOWN INTO
A TROUGH AXIS FROM S ALABAMA TO 23N95.5W.  SLIGHTLY DIVERGENT
FLOW E OF THE TROUGH COMBINED WITH A SURFACE TROUGH THAT
SEPARATED FROM A TROPICAL WAVE YESTERDAY WITH CAUSING WIDELY
SCATTERED SHOWERS WITH A FEW TSTMS FROM 23N-26N BETWEEN
85W-95W.  UPPER RIDGING COVERS THE SW CARIBBEAN WITH
OCCASIONALLY CONVECTION IN THE BAY OF CAMPECHE SPAWNED FROM
OVERNIGHT TSTMS OVER YUCATAN.  TSTMS OVER S FLORIDA AND THE
FLORIDA STRAITS ARE BEING CAUSED BY A MID/UPPER LOW JUST W OF
ANDROS ISLAND.  THIS UPPER LOW IS FORECAST TO MOVES INTO THE SE
GULF TOMORROW.. WHICH COULD HELP PRODUCE AN ACTIVE CONVECTION
DAY OVER S FLORIDA... THOUGH THERE ISN'T MUCH MOISTURE ALOFT
WITH THE SYSTEM.  WEAK HIGH PRESSURE OVER FLORIDA IS KEEPING
LIGHT WINDS OVER THE AREA WITH THE STRONGEST WINDS IN THE FAR SW
GULF.  STANDARD SUMMERTIME CONVECTION LOOKS TO BE THE RULE
ACROSS THE GULF COAST WITH THE UPPER TROUGH SLOWLY DIMINISHING.

CARIBBEAN SEA...
UPPER TROUGH EXTENDS FROM CENTRAL CUBA BETWEEN THE CAYMANS AND
JAMAICA SOUTHWARD TO 11N79W MOVING SLOWLY WESTWARD.  MODERATE/
STRONG SUBSIDENCE IS KEEPING MOST OF THE W CARIBBEAN WITHOUT
SIGNIFICANT CONVECTION EXCEPT NEAR DIVERGENCE AT THE BASE OF THE
TROUGH WHERE IT INTERSECTS THE ITCZ AND WIDELY SCATTERED TSTMS
ARE S OF 11N BETWEEN 75W-81W.  THIS TROUGH IS ALSO ENHANCING A
TROPICAL WAVE'S CONVECTION ALONG 76W.  IN THE E CARIBBEAN...
UPPER RIDGE LIES FROM PUERTO RICO TO THE ABC ISLANDS WITH A
SHOWERY DAY W OF 62W N OF 13W DUE TO A FAST-MOVING TROPICAL
WAVE.   SUNDAY LOOKS TO BE THE DRIEST DAY IN THE LESSER ANTILLES
BEFORE INCREASING MOISTURE OVERSPREADS THE WINDWARD ISLANDS LATE
SUN... AS FAR N AS GUADELOUPE BY TUE.

ATLANTIC OCEAN...
THE AREA CONTINUES TO BE DOMINATED BY UPPER LOWS AND TROUGH
UNLIKE THE BIG RIDGES THAT WERE SEEN EARLIER IN THE SEASON.
FIRST UPPER LOW IS MOVING THRU THE NW BAHAMAS INTO THE GULF
MEXICO.  RIDGING IS IN BETWEEN FROM 31N66W SW OF BERMUDA THRU
PUERTO RICO KEEPING THINGS RELATIVELY DRY EXCEPT FOR A DISTANT
BAND OF IRENE WITHIN 30 NM OF 26N69W 30N66W 32N66W.  DEEP
MID-OCEANIC TROUGH EXTENDS FROM A CLOSED LOW NEAR 30N42W SW TO
13N54W IN THE W TROPICAL ATLC.  THIS TROUGH IS RATHER CLOSE TO
THE SYSTEM NEAR 44W AND COULD INCREASE SHEAR DURING THE NEXT FEW
DAYS.  FARTHER E...HIGH-AMPLITUDE RIDGE EXTENDS FROM A HIGH OVER
W MAURITANIA THRU THE CANARY ISLANDS WITH MID/UPPER MOISTURE
SPREADING NORTHWARD IN THE NE ATLC...THOUGH APPARENTLY NOT
CAUSING ANY RAIN.  IN THE DEEP TROPICS... UPPER RIDGE LIES FROM
W MAURITANIA TO 14N48W BROKEN BY AN INVERTED TROUGH FROM 10N32W
TO 30N31W...PROBABLY THE REFLECTION OF THE STRONG TROPICAL WAVE
W OF THE CAPE VERDES.  SURFACE PRESSURE IS BELOW AVERAGE IN THE
DEEP TROPICS WITH THE SUBTROPICAL RIDGE FAR TO THE N AND QUITE
WEAK...LEADING TO LIGHT TRADES.  IN FACT WHERE THE RIDGE USUALLY
IS...A PAIR OF 1017 MB LOWS ARE POSITIONED NEAR 29N39W AND
27N46W WITH A FEW TSTMS WITHIN 60 NM OF THE LOWS.  HOWEVER THE
GFS SUGGESTS TRADES WILL SIGNIFICANTLY INCREASE IN THE E AND
CENTRAL ATLC BEHIND THE TROPICAL WAVE AS THE LOWS DISSIPATE AND
THE ATLC RIDGE BUILDS IN.  STRONG WLY LOW-LEVEL FLOW CONTINUES
IN THE E ATLC... CAUSING PLENTY OF ITCZ CONVECTION.

$$
BLAKE

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