[Tropical] Tropical Weather Discussion

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AXNT20 KNHC 281802
TWDAT

TROPICAL WEATHER DISCUSSION
NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL
205 PM EDT SUN AUG 28 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 POTENTIALLY CATASTROPHIC CATEGORY FIVE HURRICANE
KATRINA IS NEAR 26.5N 88.6W AT 28/1800 UTC...OR ABOUT 200 MILES
SOUTH OF THE MOUTH OF THE MISSISSIPPI RIVER. IT IS MOVING
NW 11 KT. THE ESTIMATED MINIMUM CENTRAL PRESSURE IS 906 MB. THE
MAXIMUM SUSTAINED WINDS ARE NEAR 150 KT WITH GUSTS TO 180 KT.
PLEASE READ THE LATEST NHC FORECAST/ADVISORY UNDER AWIPS/WMO
HEADERS MIATCMAT2/WTNT22 KNHC AND THE PUBLIC ADVISORY UNDER
AWIPS/WMO HEADERS MIATCPAT2/WTNT32 KNHC FOR MORE DETAILS.
KATRINA HAS STRENGTHENED RAPIDLY OVERNIGHT INTO A CATEGORY 5
HURRICANE OVER THE VERY WARM AND DEEP LOOP CURRENT OF THE GULF
OF MEXICO.  THE HURRICANE HAS AN ANNULAR APPEARANCE ON SATELLITE
WITH A WELL-DEFINED EYE AND SYMMETRIC OUTFLOW PATTERN...
REFLECTIVE OF NEAR ZERO SHEAR.  THIS IS THE MOST SIGNIFICANT
THREAT TO THE GULF COAST SINCE HURRICANE CAMILLE OF 1969.
NUMEROUS STRONG CONVECTION WITHIN 90 NM IN THE NRN SEMICIRCLE
AND SCATTERED/NUMEROUS STRONG WITHIN 150 NM IN THE SRN
SEMICIRCLE.

CENTRAL ATLC TROPICAL WAVE ALONG 45W S OF 20N WITH A 1009 MB LOW
ALONG THE WAVE NEAR 13N.  VISIBLE IMAGES SHOW THE LOW IS FARTHER
N THAN THE 12Z ANALYSIS NEAR 15N46W AS BUOY 41041 IS NOW
REPORTING SW WINDS AND A PRESSURE NEAR 1008 MB.  THE SYSTEM IS
VERY NEAR TROPICAL DEPRESSION STATUS BUT ELY SHEAR COULD HINDER
DEVELOPMENT INITIALLY THOUGH IT IS EXPECTED TO DIMINISH IN A DAY
OR TWO.  THIS SYSTEM HAS THE POTENTIAL TO BE A TROPICAL CYCLONE
IN THE NEXT DAY OR TWO.  SCATTERED MODERATE CONVECTION FROM
12.5N-16.5N BETWEEN 46W-51W.

E ATLC WAVE IS ALONG 19W S OF 18N WITH A 1010 MB LOW ALONG THE
WAVE NEAR 9.5N.  VISIBLE SATELLITE SHOWS THAT THIS SYSTEM HAS
WELL-DEFINED CURVED BANDS WITH LITTLE VERTICAL WIND SHEAR
APPARENT FROM CIRRUS CLOUDS.  THIS SYSTEM ALSO HAS THE POTENTIAL
TO BE A TROPICAL CYCLONE IN THE NEXT DAY OR TWO.

...TROPICAL WAVES...

W ATLC WAVE IS ALONG 57W SOUTH OF 19N MOVING W 10 KT. AN EARLIER
LOW PRESSURE SYSTEM HAS OPENED UP INTO A TROUGH.  STRONG SHEAR
PREVENTED THIS SYSTEM FROM DEVELOPING AND IT NOW HAS A WEAK
SIGNATURE ON SATELLITE.

...ITCZ...

ITCZ AXIS IS ALONG 9N13W 7N27W 15N38W 9N49W 12N54W.  THE ITCZ IS
NOT WELL-DEFINED AT ALL TODAY.  ISOLATED TSTMS ARE WITHIN 60 NM
OF AXIS BETWEEN 22W-29W AND FROM 7N-10N BETWEEN 48W-54W.

...DISCUSSION...

GULF OF MEXICO...
KATRINA DOMINATES THE GULF WITH A TREMENDOUS CIRCULATION IN THE
LOW TO MID-LEVELS.  SEE SPECIAL FEATURES FOR MORE DETAILS.  THE
RAINBANDS ARE NOW SOUTH OF LAKE PONTCHARTRAIN IN LOUISIANA AND
SHOULD SLOWLY OVERSPREAD MISSISSIPPI AND THE REST OF THE SE
LOUISIANA THIS AFTERNOON.  A LARGE UPPER LEVEL ANTICYCLONE IS
CONTROLS THE AREA WITH A WELL-DEFINED CYCLONIC CIRCULATION NOTED
IN UPPER LEVELS RIGHT OVER THE STORM.  RELATIVELY MOIST
CONDITIONS SHOULD SUPPORT DAILY DIURNAL TSTMS OVER THE FLORIDA
PENINSULA WITH A MID/UPPER DRY AIR KEEPING THINGS QUIET OVER
TEXAS.

CARIBBEAN SEA...
DEEP LAYERED ELYS ARE OVER THE AREA EXCEPT FOR AN UPPER TROUGH
FROM 20N67W TO HAITI.  A BIT OF UPPER DIVERGENCE NEAR THE TROUGH
ALONG WITH A WEAK TROUGH IS FORCING ISOLATED TSTMS S OF
HISPANIOLA TO 15N BETWEEN 71W77W.  THIS MOISTURE SHOULD MOVE
INTO JAMAICA OVERNIGHT WITH AN ENHANCED CHANCE OF RAIN.
OTHERWISE DRY AIR IN THE MID/UPPER LEVELS IS KEEPING THINGS
RELATIVELY QUIET IN THE LESSER ANTILLES BUT INCREASING MOISTURE
FROM THE SYSTEM NEAR 45W SHOULD ARRIVE AROUND TUESDAY.  TRADES
ARE VERY LIGHT WITH THE ABSENCE OF THE SUBTROPICAL RIDGE DUE TO
KATRINA AND THE ITCZ POSITION FAR TO THE NORTH OVER THE ATLC.

ATLANTIC OCEAN...
UPPER TROUGH EXTENDS FROM 32N57W TO 23N60W THEN SW TO
HISPANIOLA.  NLY SHEAR IS PREVENTING THE DEVELOPMENT OF A SMALL
LOW JUST OFFSHORE OF CAPE FEAR N CAROLINA AS WELL AS A WEAK
TROUGH N OF THE BAHAMAS ALONG 26N BETWEEN 72W-77W.  HOWEVER THIS
IS A FAVORABLE PATTERN FOR TSTM DEVELOPMENT WITH ISOLATED TO
WIDELY SCATTERED TSTMS N OF 25N BETWEEN BERMUDA AND 76W.  NARROW
UPPER RIDGE LIES ALONG 48W N OF 20N WITH A PERSISTENT UPPER
TROUGH CONTROLLING THE AREA N OF 27N E OF 40W.  IN THE DEEP
TROPICS... UPPER HIGH IS NEAR 15N47W... PROVIDING ELY SHEAR OVER
THE DISTURBANCE NEAR 45W.  MODERATE/STRONG SUBSIDENCE IS S OF
20N E OF THE DISTURBANCE TO 30W WITH A SAHARAN DUST OUTBREAK
NOTED.  SE OF THE CAPE VERDES... MOISTURE INCREASES WITH UPPER
RIDGING SUPPRESSED FROM GAMBIA TO 11N30W.  ITCZ CONVECTION IS
MINIMAL WITH NO LOW-LEVEL CONVERGENCE AS ALL THE TROPICAL
WAVES/SYSTEMS ARE DOMINATING THE CIRCULATION.

$$
BLAKE

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