[Tropical] Tropical Weather Discussion

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AXNT20 KNHC 121758
TWDAT

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

...SPECIAL FEATURE...

TROPICAL STORM IRENE IS CENTERED NEAR 28.3N 66.8W...OR 620 NM SE
OF CAPE HATTERAS NORTH CAROLINA...AT 12/1500 UTC MOVING NW AT 11
KT. ESTIMATED MINIMUM CENTRAL PRESSURE IS 994 MB. MAXIMUM
SUSTAINED WIND SPEED IS 55 KT WITH GUSTS TO 65 KT. SEE THE
LATEST NHC FORECAST/ADVISORY UNDER AWIPS/WMO HEADERS
MIATCMAT4/WTNT24 KNHC FOR MORE DETAILS.  IRENE HAS PLENTY OF
BANDING AROUND THE CENTER WITH AN EXPANDING OUTFLOW PATTERN TO
THE NORTH.  LITTLE SHEAR IS FORECAST FOR THE NEXT SEVERAL DAYS.
COMPUTER MODELS ARE IN BETTER AGREEMENT THAN YESTERDAY ON THE
CYCLONE SNEAKING THROUGH A BREAK IN THE RIDGE AND RECURVING
BEFORE IT COULD MAKE A US LANDFALL.  HOWEVER THIS SCENARIO IS
NOT CERTAIN AND SMALL CHANGES IN THE SHORT-TERM COULD HAVE LARGE
EFFECTS DOWN THE ROAD.  FOR NOW IRENE SHOULD CONTINUE TO SLOWLY
INTENSIFY... THOUGH AFTER 24 HOURS IT COULD BE AFFECTED BY THE
COLD WAKES OF FRANKLIN AND HARVEY WHICH COOLED THE WATER TO NEAR
80-81F.   SCATTERED MODERATE CONVECTION FROM 27N-31N BETWEEN
65W-70W.

1012 MB LOW HAS DEVELOPED FROM THE TROPICAL WAVE PREVIOUSLY
ALONG 39W.  THE BROAD CENTER OF THE LOW IS NEAR 11N41W AND IS
MOVING WNW 10-15.  THIS IS A COMPLEX DISTURBANCE WITH A LOW/MID-
LEVEL CENTER SEEN ON VISIBLE SATELLITE NEAR 12N42W WITH ANOTHER
LOBE OF ENERGY ROTATING AROUND THE E SIDE NEAR 12N39W.  SURFACE
OBSERVATIONS INDICATE A LARGE CLOSED CIRCULATION WITH BUOYS
REPORTING WINDS OF 20-25 KT.  THE LOW HAS FAVORABLE CONDITIONS
FOR FURTHER DEVELOPMENT WITH WARM WATER NEAR 83F... LIGHT
SHEAR... AND IT SEEMS TO BE FAR ENOUGH SOUTH TO AVOID
SIGNIFICANT DRY AIR IN THE MID-LEVELS.  THERE IS SOME EVIDENCE
OF BANDING THOUGH CONVECTION HAS FADED A BIT THIS AFTERNOON.
ISOLATED MODERATE FROM 10N-13N BETWEEN 40W-45W.

...TROPICAL WAVES...

TROPICAL WAVE IS JUST OFF THE AFRICAN COAST ALONG 20W/21W S OF
21N MOVING W 5-10 KT WITH A 1011 MB LOW ALONG THE WAVE NEAR
15N.  THE WAVE HAD AN IMPRESSIVE SIGNATURE ON THE DAKAR
TIMESECTION WITH A WELL-DEFINED WAVE PASSAGE.  IN ADDITION THE
LOW PRESSURE SYSTEM APPEARS TO BE MUCH MORE VERTICALLY DEEP IN
THE ATMOSPHERE THAN USUAL WITH SW WINDS REPORTED UP UP TO 700 MB
THIS MORNING.  SATELLITE PICTURES SHOW A LARGE STRATOCUMULUS
SWIRL ELONGATED FROM SW TO NE WITH STRONG WLY FLOW S OF THE WAVE
IN THE LOW-LEVELS.  ANY SIGNIFICANT CONVECTION IS IN THE ITCZ.

TROPICAL WAVE PREVIOUSLY ALONG 39W IS NOW A SPECIAL FEATURE.

TROPICAL WAVE IS ALONG 58W S OF 16N MOVING W 20 KT.  24 HOUR
PRESSURE FALLS OF 1-2 MB ARE IN THE LESSER ANTILLES TODAY...
SUGGESTING THE WAVE IS APPROACHING.  INCREASING SHOWERS SHOULD
CONTINUE TO OVERSPREAD THE NORTHERN WINDWARD AND LEEWARD ISLANDS
TODAY WITH MOISTURE IMPACTING PUERTO RICO OVERNIGHT INTO
TOMORROW.  WIDELY SCATTERED SHOWERS AND A FEW TSTMS ARE FROM
13N-18N BETWEEN 56W-63W.

E CARIBBEAN TROPICAL WAVE ALONG 68W/69W S OF 19N MOVING W 10-15
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
THOUGH TSTMS OVER NW VENEZUELA MIGHT BE RELATED TO THE WAVE.

W CARIBBEAN TROPICAL WAVE IS ALONG 89W S OF 20N MOVING W 15 KT.
EARLIER TSTMS OVER CENTRAL AMERICA HAVE DISSIPATED BUT THERE IS
PLENTY OF MOISTURE AND ENERGY FOR ANOTHER ROUND PROBABLY ALONG
THE SEABREEZE THIS AFTERNOON.

...ITCZ...

ITCZ AXIS IS CENTERED ALONG 15N15N 11N22W 11N41W 12N54W.
ISOLATED MODERATE CONVECTION WITHIN 60 NM OF AXIS FROM
30W-55W.   WIDELY SCATTERED MODERATE WITHIN 75 NM OF ITCZ
BETWEEN 19W-30W.

...DISCUSSION...

GULF OF MEXICO...
PERSISTENT CUT-OFF MID/UPPER LOW DOMINATES MOST OF THE WEATHER
IN THE GULF WITH A CENTER IN SW ALABAMA TROUGHING SSW TO
24N96W.  WEAK SURFACE TROUGH ALSO SHOWS UP HELPING TO SPAWN A
FEW TSTMS FROM NW FLORIDA TO 28N90W.  UPPER DIVERGENCE E OF THE
TROUGH IS CAUSING WIDELY SCATTERED TSTMS FROM 23N-27N BETWEEN
83W-88W.  RIDGING EXTENDS IN THE UPPER LEVELS FROM YUCATAN TO SW
FLORIDA WITH BROKEN HIGH CLOUDS FROM EARLIER TSTMS COVERING THE
SOUTHERN GULF SE OF A LINE FROM TAMPICO MEXICO TO CEDAR KEY
FLORIDA.  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 SE CUBA THRU JAMAICA TO PANAMA MOVING
SLOWLY WESTWARD.  MODERATE/STRONG SUBSIDENCE IS KEEPING MOST OF
THE CARIBBEAN WITHOUT SIGNIFICANT CONVECTION EXCEPT AT THE BASE
OF THE TROUGH WHERE A FEW TSTMS ARE S OF 11N W OF 78W.  WIDELY
SCATTERED TSTMS ARE CLOSE TO A FORMING UPPER LOW BETWEEN CUBA
AND JAMAICA ALONG THE TROUGH AXIS.  UPPER RIDGING CONTINUES TO
NOSE INTO THE E CARIBBEAN FROM GUADELOUPE TO THE ABC ISLANDS
THOUGH INCREASING MOISTURE FROM A TROPICAL WAVE IS CAUSING A
WETTER-THAN-AVERAGE DAY IN THE LESSER ANTILLES.  THE BACK EDGE
OF THE MOISTURE SHOULD REACH THE E CARIBBEAN DURING THE DAY
TOMORROW AND PROBABLY BRING A DRIER DAY.

ATLANTIC OCEAN...
PAIR OF UPPER LOWS ARE OVER THE W ATLC... S AND SW OF IRENE.
ONE IS NEAR THE NW BAHAMAS MOVING SW... WHILE THE OTHER IS NEAR
25N67W.  IRENE ROTATED IS N OF THE LAST UPPER LOW... WITH
GENERAL SE FLOW ALOFT.  MODERATE SUBSIDENCE S OF IRENE TO PUERTO
RICO BETWEEN 62W-75W IS KEEPING MOST SIGNIFICANT CONVECTION TO A
MINIMUM.  UPPER RIDGE AXIS LIES FROM A HIGH CENTER NEAR 30N64W
RIDGING SSW TO 14N59W...ASSISTING IRENE.  A RATHER DEEP
MID-OCEANIC TROUGH IS SETTING UP IN THE CENTRAL ATLC FROM A LOW
NEAR 33N43W SSW TO 18N50W.  THE TROUGH IS FORECAST TO CONTINUE
DIGGING... EXTENDING FAR INTO THE TROPICS TOMORROW AND MAY
AFFECT THE FUTURE DEVELOPMENT OF THE SYSTEM NEAR 11N41W.  A
DISTURBANCE DROPPING INTO THE NORTHERN PORTION OF THAT TROUGH...
1019 MB LOW NEAR 29N45W... IS FIRING A FEW TSTMS WITHIN 90 NM OF
THE LOW.  BROAD UPPER TROUGHING COVERS THE E-CENTRAL ATLC TO
25W.  STRONG UPPER RIDGING HAS BUILT UP IN THE NE ATLC FROM W
AFRICA THRU THE CANARY ISLANDS WITH A SURGE OF MID/UPPER
MOISTURE N OF 20N TO THE CANARYS E OF 22W.  IN THE DEEP
TROPICS... UPPER RIDGE LIES FROM W AFRICA TO 15N50W BROKEN BY AN
INVERTED TROUGH JUST W OF THE CAPE VERDE ISLANDS.. PROBABLY THE
REFLECTION OF A STRONG TROPICAL WAVE.  SHEAR IS SLIGHTLY BELOW
AVERAGE IN THE DEEP TROPICS ALONG WITH THE SURFACE PRESSURE.
HOWEVER THE GFS SUGGESTS SHEAR WILL SIGNIFICANTLY INCREASE W OF
50W FOR THE NEXT SEVERAL DAYS AS THE MID-OCEANIC TROUGH LOCKS
INTO PLACE.

$$
BLAKE

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