[Tropical] Tropical Weather Discussion

[EMWIN Server]

AXNT20 KNHC 122356
TWDAT

TROPICAL WEATHER DISCUSSION
NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL
805 PM EDT FRI AUG 12 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.

...SPECIAL FEATURE...

TROPICAL STORM IRENE IS CENTERED NEAR 28.7N 67.5W...OR 565 NM SE
OF CAPE HATTERAS NORTH CAROLINA...AT 12/2100 UTC MOVING NW AT 9
KT. ESTIMATED MINIMUM CENTRAL PRESSURE IS 997 MB. MAXIMUM
SUSTAINED WIND SPEED IS 60 KT WITH GUSTS TO 75 KT. SEE THE
LATEST NHC FORECAST/ADVISORY UNDER AWIPS/WMO HEADERS
MIATCMAT4/WTNT24 KNHC FOR MORE DETAILS. IRENE HAS STRENGTHENED
DURING THE AFTERNOON HOURS ACCORDING TO DATA FROM A
RECONNAISSANCE AIRCRAFT. THIS IS SUPPORTED BY SATELLITE IMAGERY
WHICH INDICATE BANDING DEVELOPING AROUND A CENTRAL DENSE
OVERCAST. OUTFLOW PATTERN IS EXPANDING TO THE WEST AND
NORTH...AN INDICATION OF THE STEERING CURRENTS AROUND IRENE.
THE STORM IS BEING STEERED BY HIGH PRESSURE EAST OF BERMUDA AND
LOW PRESSURE JUST E OF THE NORTHERN BAHAMAS. LITTLE SHEAR IS
FORECAST FOR THE NEXT SEVERAL DAYS AND IRENE IS FORECAST TO
BECOME A HURRICANE DURING THE NEXT 12-24 HOURS AS IT MOVES NW
TOWARD A WEAKNESS IN THE SUBTROPICAL RIDGE CURRENTLY ABOUT 200
NM SE OF CAPE HATTERAS. COMPUTER MODELS ARE IN GOOD AGREEMENT ON
TAKING IRENE TO THE WEAKNESS IN THE RIDGE...THEN RECURVING THE
CYCLONE AWAY FROM THE U.S. COAST. HOWEVER THIS SCENARIO IS NOT
CERTAIN AND SMALL CHANGES IN THE SHORT-TERM COULD HAVE LARGE
EFFECTS DOWN THE ROAD. NUMEROUS MODERATE/SCATTERED STRONG
CONVECTION IS WITHIN 100 NM SE AND S QUADRANTS...WITH SCATTERED
MODERATE CONVECTION ELSEWHERE WITHIN 120 NM OF CENTER.

1010 MB LOW NEAR 12N42W IS MOVING WNW 10-15 KT. THE LOW LIES
ALONG A TROPICAL WAVE WHICH EXTENDS FROM 17N41-6N43W. THE LOW
HAS BECOME BETTER ORGANIZED DURING THE DAY...WITH HINTS OF
BANDING IN THE N SEMICIRCLE...WHERE SCATTERED MODERATE
CONVECTION IS NOTED WITHIN ABOUT 150 NM OF THE CENTER. THE LOW
HAS SEPARATED FROM THE ITCZ WHICH IS USUALLY FAVORABLE FOR
STRENGTHENING. UPPER LEVEL WINDS ARE ALSO FAVORABLE FOR
DEVELOPMENT...ALTHOUGH A MID/UPPER LEVEL TROUGH WITH ITS BASE
NEAR 18N49W IS SLOWLY APPROACHING THE LOW.

...TROPICAL WAVES...

TROPICAL WAVE IS BETWEEN THE AFRICAN COAST AND THE CAPE VERDE
ISLANDS ALONG 21W S OF 21N MOVING W 5-10 KT...WITH A 1010 MB LOW
ALONG THE WAVE NEAR 15N.  LITTLE CHANGE IN STRUCTURE HAS BEEN
OBSERVED DURING THE AFTERNOON HOURS...WITH A LARGE STRATOCUMULUS
SWIRL SURROUNDING THE LOW. NO DEEP CONVECTION IS NOTED WITH THE
LOW...AND ANY SIGNIFICANT CONVECTION IS IN THE ITCZ.

TROPICAL WAVE IS ALONG 59W/60W S OF 18N MOVING W 20 KT. SURFACE
OBSERVATIONS FROM THE LESSER ANTILLES AND SATELLITE TRENDS
INDICATE THAT THE WAVE IS PASSING OVER THE LESSER ANTILLES...
WITH SCATTERED SHOWERS AND TSTMS AFFECTING MUCH OF THE ISLANDS
FROM ST. VINCENT NORTHWARD TO GUADELOUPE. THIS ACTIVITY IS
EXPECTED TO SPREAD NW TO THE NORTHERN LEEWARD ISLANDS AND PUERTO
RICO DURING THE NEXT 24 HOURS.

E CARIBBEAN TROPICAL WAVE ALONG 70W S OF 19N MOVING W 15 KT.
THERE ARE SOME HINTS OF THE WAVE WITH CURVATURE IN THE LOW
CLOUDS BUT THE POSITION IS MOSTLY BASED ON EXTRAPOLATION AND
LONG-TERM SATELLITE LOOPS.  NO SIGNIFICANT CONVECTION OVER
WATER...ALTHOUGH TSTMS OVER HISPANIOLA AND NORTHWESTERN
VENEZUELA MIGHT BE ENHANCED BY THE WAVE.

TROPICAL WAVE PREVIOUSLY ALONG 89W S OF 20N HAS SPLIT...WITH THE
MAIN PORTION OF THE WAVE OVER THE PACIFIC S OF GUATEMALA AND SE
MEXICO...AND A REMNANT TROUGH OVER THE EASTERN GULF OF MEXICO.

...ITCZ...

ITCZ AXIS IS CENTERED ALONG 7N12W 13N16W 10N25W 10N31W 12N39W
8N50W 12N57W. SCATTERED MODERATE CONVECTION IS WITHIN 60 NM OF
AXIS BETWEEN 22W-29W...AND BETWEEN 46W-51W. ISOLATED MODERATE
CONVECTION IS WITHIN 60 NM OF AXIS BETWEEN 53W-56W.

...DISCUSSION...

GULF OF MEXICO...
PERSISTENT CUT-OFF LOW IS OVER THE SE UNITED STATES OVER
MISSISSIPPI...WITH A TROUGH SSW ACROSS LOUISIANA TO THE MEXICAN
COAST NEAR 23N97W. INSTABILITY ASSOCIATED WITH THE CUT-OFF LOW
CONTINUES TO SPARK SCATTERED SHOWERS AND TSTMS FROM GEORGIA
WESTWARD TO LOUISIANA. AT THE SURFACE...A TROUGH EXTENDS FROM
29N85W-21N91W WITH WIDELY SCATTERED SHOWERS/TSTMS ALONG THE
TROUGH. NARROW MID/UPPER LEVEL RIDGE IS OVER THE E GULF FROM THE
YUCATAN PENINSULA TO THE FLORIDA BIG BEND. UPPER DIFFLUENCE
ASSOCIATED WITH THE RIDGE IS ENHANCING DIURNAL CONVECTION OVER
THE CENTRAL FLORIDA PENINSULA. LITTLE SIGNIFICANT CHANGE IS
LIKELY WITH THE BROAD LOW NEARLY STATIONARY...ENHANCING DAILY
TSTMS ALONG THE NRN GULF COAST.

CARIBBEAN SEA...
UPPER TROUGH EXTENDS FROM E CENTRAL CUBA THRU JAMAICA TO NEAR
13N79W...MOVING SLOWLY WESTWARD. ISOLATED TSTMS ARE OCCURRING
ALONG THE TROUGH AXIS OVER E CUBA AND JAMAICA...WITH ADDITIONAL
ISOLATED TSTMS ABOUT 90 NM S OF GRAND CAYMAN...AND OVER THE FAR
SW CARIBBEAN ALONG 11N BETWEEN 79W-82W. MID/UPPER LEVEL RIDGING
IS ESTABLISHED OVER THE E CARIBBEAN...WITH AN ANTICYCLONIC
CIRCULATION NOTED OVER THE LEEWARD ISLANDS. SLY FLOW BETWEEN THE
RIDGE AND THE W CARIBBEAN LOW IS ADVECTING HIGH LEVEL MOISTURE
NORTHWARD FROM SOUTH AMERICA ACROSS THE CARIBBEAN TO HISPANIOLA.
UPPER DIFFLUENCE ASSOCIATED WITH THE RIDGE AND ANTICYCLONE IS
SUPPORTING SCATTERED TSTMS ASSOCIATED WITH TROPICAL WAVE OVER
THE ISLANDS.

ATLANTIC OCEAN...
PAIR OF UPPER LOWS ARE OVER THE W ATLC...S AND SW OF IRENE.
ONE IS NEAR THE NW BAHAMAS NEAR 26N76W MOVING SW WHICH MARKS THE
NORTHERN EXTENT OF THE W CARIBBEAN UPPER TROUGH...WHILE THE
OTHER IS ROTATING NORTHWARD OVER THE CIRCULATION OF IRENE NEAR
27N68W. SUBSIDENCE WITH THE LOW NEAR 27N68W IS LIMITING
CONVECTION AND OUTFLOW IN THE S QUADRANT OF IRENE...WITH GENERAL
SE FLOW ALOFT OVER THE TROPICAL CYCLONE. UPPER RIDGE AXIS LIES
FROM A HIGH CENTER E OF BERMUDA NEAR 30N62W SSW TO THE
ANTICYCLONE OVER THE LESSER ANTILLES. A RATHER DEEP MID-OCEANIC
TROUGH IS SETTING UP IN THE CENTRAL ATLC FROM A LOW NEAR 31N43W
SSW TO 18N49W. THE TROUGH IS FORECAST TO REMAIN NEARLY
STATIONARY BUT DIG SW TO NEAR 15N52W IN ABOUT 24 HOURS. THIS
COULD AFFECT THE FUTURE DEVELOPMENT OF THE SURFACE LOW NEAR
12N42W. A 1018 MB LOW NEAR 29N45W IS DRIFTING SW AND SETTING OFF
ISOLATED TSTMS WITHIN 60 NM OF THE LOW. BROAD UPPER TROUGH
COVERS THE FAR N PORTION OF E-CENTRAL ATLC N OF 28N BETWEEN
25W-35W. MUCH OF THE E ATLC IS DOMINATED BY HIGH PRES
ALOFT...WITH ONE CENTER NEAR 19N33W AND THE OTHER OVER W AFRICA
NEAR 21N12W. BETWEEN THE TWO HIGHS...A WEAK TROUGH/COL REGION
EXTENDS FROM 24N23W-13N27W. THIS COL REGION MARKS THE LEADING
EDGE OF THE MOISTURE SURGE ASSOCIATED WITH THE TROPICAL WAVE AND
LOW PRES ALONG 21W. RIDGE WILL BECOME ESTABLISHED E OF 30W AS
THE HIGH NEAR 19N33W WEAKENS...KEEPING ELY FLOW AND LIGHT SHEAR
OVER FAR E ATLC. SHEAR WILL GRADUALLY INCREASE W OF 30W IN
ASSOCIATION WITH THE SOUTHERN PORTION OF THE MID-OCEANIC TROUGH
FROM 20N50W-15N52W.

$$
MOLLEDA


This weather bulletin was brought to you by:
www.nashvilleweather.net