Hurricane Isaac Discussion #31

000
WTNT44 KNHC 282053
TCDAT4

HURRICANE ISAAC DISCUSSION NUMBER  31
NWS NATIONAL HURRICANE CENTER MIAMI FL  AL092012
400 PM CDT TUE AUG 28 2012

SINCE THE LAST RECON FLIGHTS INTO 
ISAAC...WHEN A BIAS-CORRECTED SFMR WIND 
OF 64 KT WAS OBSERVED...THE RADAR AND 
SATELLITE APPEARANCE HAS CONTINUED TO 
BECOME BETTER DEFINED. ON THIS 
BASIS...THE ESTIMATED  INTENSITY HAS BEEN 
INCREASED TO 70 KT.

TRENDING THROUGH ALL OF THE WIGGLES 
AND WOBBLES IN THE AIRCRAFT FIXES YIELDS 
A GENERAL NORTHWESTWARD MOTION OF 
310/07 KT. ISAAC REMAINS ON TRACK...AND 
THERE HAS BEEN NO SIGNIFICANT CHANGE TO 
THE EARLY PART OF THE FORECAST. ISSAC IS 
EXPECTED TO CONTINUE NORTHWESTWARD 
TOWARD A WEAKNESS IN THE SUBTROPICAL 
RIDGE THAT IS ORIENTED EAST-WEST ALONG 
30N LATITUDE. BECAUSE OF THIS WEAKNESS... 
THE STEERING FLOW IS FORECAST TO 
DECREASE OVER THE NEXT 36-48 
HOURS...WHICH WILL RESULT IN ISAAC 
SLOWING DOWN SOME MORE. 
AFTERWARDS...THE RIDGE IS FORECAST TO 
BUILD BACK IN BY ALL OF THE 
MODELS...ALBEIT TO VARYING 
DEGREES...WHICH SHOULD CAUSE THE 
CYCLONE TO TURN SLIGHTLY TOWARD THE 
WEST-NORTHWEST BEFORE IT TURNS 
NORTHWARD BY DAY 4...AND THEN MOVE 
NORTHEASTWARD INTO THE LOWER GREAT 
LAKES AND OHIO VALLEY REGIONS BY DAY 5. 
IN THE LATTER PART OF THE FORECAST 
PERIOD THE FORECAST HAS BEEN NUDGED A 
LITTLE TO THE LEFT OF THE PREVIOUS 
TRACK...BUT REMAINS TO THE RIGHT OF THE 
CONSENSUS MODELS THAT HAVE RECENTLY 
HAD A LEFTWARD BIAS.

ALTHOUGH NOT EXPLICITLY FORECAST DUE 
TO LAND INTERACTION AT 12 
HOURS...FAVORABLE WATER TEMPERATURES 
ALONG WITH AN IMPRESSIVE UPPER-LEVEL 
OUTFLOW REGIME SUGGEST THAT ISAAC 
COULD STRENGTHEN A LITTLE MORE BEFORE 
LANDFALL OCCURS.  HOWEVER...BECAUSE OF 
THE UNUSUALLY LARGE WIND FIELD...RAPID 
INTENSIFICATION IS NOT EXPECTED.

ISAAC REMAINS A LARGE TROPICAL CYCLONE. 
A DANGEROUS STORM SURGE...HEAVY 
RAINFALL...AND STRONG WINDS EXTEND WELL 
AWAY FROM THE CENTER AND ARE EXPECTED 
TO AFFECT A LARGE PORTION OF THE 
NORTHERN GULF COAST. FOR THIS REASON...IT 
IS IMPORTANT NOT TO FOCUS ON THE EXACT 
CENTER LOCATION. THE THREAT OF HEAVY 
RAINFALL AND FLOODING IS ALSO EXPECTED 
TO SPREAD INLAND OVER THE LOWER 
MISSISSIPPI VALLEY REGION DURING THE 
NEXT FEW DAYS.

FORECAST POSITIONS AND MAX WINDS

INIT  28/2100Z 28.7N  89.2W   70 KT  80 MPH
 12H  29/0600Z 29.4N  90.0W   70 KT  80 MPH
...INLAND
 24H  29/1800Z 30.3N  91.0W   55 KT  65 MPH
...INLAND
 36H  30/0600Z 31.3N  91.9W   35 KT  40 MPH
...INLAND
 48H  30/1800Z 33.0N  92.5W   30 KT  35 MPH
...INLAND
 72H  31/1800Z 36.0N  92.5W   20 KT  25 MPH
...INLAND
 96H  01/1800Z 39.0N  90.5W   15 KT  15 MPH
...POST-TROP/REMNT LOW
120H  02/1800Z 41.5N  86.5W   15 KT  15 MPH
...POST-TROP/REMNT LOW

$$
FORECASTER STEWART

T.S. Isaac Discussion #27

000
WTNT44 KNHC 272058
TCDAT4

TROPICAL STORM ISAAC DISCUSSION NUMBER  27
NWS NATIONAL HURRICANE CENTER MIAMI FL  AL092012
400 PM CDT MON AUG 27 2012

THE MUCH ANTICIPATED INTENSIFICATION 
PROCESS APPEARS TO HAVE FINALLY 
STARTED BASED ON REPORTS FROM AN AIR 
FORCE RESERVE RECONNAISSANCE 
AIRCRAFT AND FROM NEARBY NOAA BUOY 
42003. THE CENTRAL PRESSURE HAS 
DECREASED BY AT LEAST 7 MB SINCE THE 
PREVIOUS ADVISORY. THE HIGHEST FLIGHT-
LEVEL WINDS OBSERVED HAVE BEEN 74 KT 
IN THE SOUTHWEST QUADRANT AND THE 
HIGHEST BIAS-ADJUSTED SFMR WINDS ARE 
NEAR 58 KT. THESE DATA SUPPORT AN 
INTENSITY OF 60 KT.

ISAAC WOBBLED WESTWARD THIS 
AFTERNOON...BUT A REPRESENTATIVE 
INITIAL MOTION ESTIMATE IS 305/10. THE 
LATEST 12Z NHC MODEL GUIDANCE IS IN 
BETTER AGREEMENT ON A WEST-
NORTHWEST TO NORTHWEST MOTION 
TOWARD THE SOUTHEAST LOUISIANA AND 
MISSISSIPPI COASTAL AREAS OVER THE 
NEXT 36-48 HOURS. AFTER 48 
HOURS...HOWEVER...THE MODEL GUIDANCE 
REMAINS DIVERGENT ON THE HANDLING OF 
A SHORTWAVE TROUGH FORECAST TO DIG 
SOUTHEASTWARD FROM THE UPPER 
MIDWEST AND INTO THE MID-ATLANTIC 
REGION...FOLLOWED BY A RIDGE BUILDING 
IN BEHIND THE TROUGH. THE GFS AND 
ECMWF...OUR MOST RELIABLE MODELS... 
NOW HAVE VERY SIMILAR SOLUTIONS 
THROUGH DAY 5...AND THE OFFICIAL 
FORECAST TRACK IS BETWEEN THOSE TWO 
MODELS.

SATELLITE DATA INDICATE ISAAC HAS 
BECOME BETTER ORGANIZED OVER THE 
PAST 6 HOURS WITH THE DEVELOPMENT OF 
A CENTRAL DENSE OVERCAST CLOUD 
PATTERN OVER THE CENTER ALONG WITH A 
DEVELOPING EYE IN RECON DATA. 
SATELLITE DATA T-NUMBERS HAVE 
INCREASED TO T4.5/77 KT FROM TAFB AND 
SAB. RECON WIND DATA INDICATE THE 
RADIUS OF MAXIMUM WINDS HAS ALSO 
PULLED INWARD TO ABOUT 30 N MI. 
ALTHOUGH ADDITIONAL CONVECTION HAS 
BEEN DEVELOPING IN THE NORTHEASTERN 
QUADRANT...DRY MID-LEVEL AIR STILL 
LURKS JUST TO THE EAST AND SOUTHEAST 
OF THE CDO FEATURE... WHICH COULD BE 
ENTRAINED INTO THE INNER CORE AT ANY 
TIME AND DISRUPT THE DEVELOPMENT 
PROCESS. DUE TO THE PROXIMITY OF DRY 
AIR...THE INTENSITY FORECAST INDICATES 
ONLY MODEST DEVELOPMENT FOR THE 
NEXT 24 HOURS. 

HOWEVER...STRENGTHENING IS EXPECTED 
TO CONTINUE  RIGHT UP UNTIL LANDFALL 
OCCURS DUE TO THE VERY WARM WATERS 
THE CYCLONE WILL BE PASSING OVER AND 
THE VERY FAVORABLE UPPER-LEVEL 
OUTFLOW REGIME THAT ISAAC IS 
FORECAST TO DEVELOP BY 24 HOURS. THE 
INTENSITY FORECAST IS JUST SLIGHTLY 
HIGHER THAN THE MODEL GUIDANCE.

BECAUSE SIGNIFICANT HAZARDS EXTEND 
WELL AWAY FROM THE CENTER...IT IS 
IMPORTANT NOT TO FOCUS ON THE EXACT 
FORECAST TRACK. THE SLOW FORWARD 
SPED OF AROUND 5 KT AFTER LANDFALL 
WILL RESULT IN A HEAVY RAIN AND FLOOD 
SITUATION FOR PORTIONS OF THE CENTRAL 
GULF COAST AND LOWER MISSISSIPPI 
VALLEY REGIONS.

FORECAST POSITIONS AND MAX WINDS

INIT  27/2100Z 26.4N  86.2W   60 KT  70 MPH
 12H  28/0600Z 27.4N  87.5W   70 KT  80 MPH
 24H  28/1800Z 28.6N  89.0W   80 KT  90 MPH
 36H  29/0600Z 29.5N  90.0W   85 KT 100 MPH...NEAR THE COAST
 48H  29/1800Z 30.3N  90.7W   75 KT  85 MPH...INLAND
 72H  30/1800Z 32.2N  91.8W   35 KT  40 MPH...INLAND
 96H  31/1800Z 35.9N  92.1W   25 KT  30 MPH...INLAND
120H  01/1800Z 38.7N  89.3W   20 KT  25 MPH...INLAND

$$
FORECASTER STEWART

T.S. Isaac Discussion #23

000
WTNT44 KNHC 262102
TCDAT4

TROPICAL STORM ISAAC DISCUSSION NUMBER  23
NWS NATIONAL HURRICANE CENTER MIAMI FL  AL092012
500 PM EDT SUN AUG 26 2012

ALTHOUGH SATELLITE AND RADAR IMAGES 
HAVE SUGGESTED THAT THE TROPICAL
CYCLONE WAS BECOMING A LITTLE BETTER 
ORGANIZED...AN AIR FORCE HURRICANE 
HUNTER AIRCRAFT INVESTIGATING ISAAC 
THIS AFTERNOON HAVE FOUND THAT THERE 
HAS BEEN NO STRENGTHENING OF THE STORM. 
FLIGHT-LEVEL AND SFMR-OBSERVED WINDS 
SUPPORT AN INTENSITY OF 50 KT. THERE IS 
STILL A WELL-ESTABLISHED UPPER-LEVEL 
OUTFLOW PATTERN OVER THE SYSTEM...
AND VERTICAL SHEAR SHOULD REMAIN 
FAIRLY LIGHT FOR THE NEXT COUPLE OF 
DAYS.  INTENSIFICATION STILL SEEMS LIKELY
AS ISAAC MOVES OVER THE EASTERN GULF...
AND  POSSIBLY OVER THE HIGHER HEAT
CONTENT OF THE LOOP CURRENT.  THE 
OFFICIAL INTENSITY FOREAST IS CLOSE TO 
THE LATEST LGEM GUIDANCE...AND NOT 
MUCH DIFFERENT FROM THE PREVIOUS 
NHC FORECAST.    

ISAAC HAS MOVED A LITTLE TO THE LEFT 
OF PREVIOUS PROJECTIONS AND CENTER 
FIXES YIELD A 6- TO 12-HOUR AVERAGED 
MOTION OF 295/15.   THE TRACK FORECAST 
CONTINUES TO BE CHALLENGING.  THE 
DYNAMICAL MODELS SHOW THE TROPICAL 
STORM/HURRICANE GRADUALLY TURNING 
TO THE RIGHT AND HEADING FOR A BREAK 
IN THE SUBTROPICAL RIDGE.  HOWEVER...
THERE ARE SUBSTANTIAL DIFFERENCES 
AMONG THE MOST RELIABLE MODELS AS 
TO WHERE ISAAC MIGHT CROSS THE
NORTHERN GULF COAST.  THE U.K. MET. 
OFFICE AND ECMWF MODELS ARE ABOUT 
300 N MI TO THE EAST OF THE GFS AT 
LANDFALL.  IT SHOULD BE NOTED THAT 
NEARLY ALL OF THE GFS ENSMEBLE  
MEMBERS ARE EAST OF THE GFS CONTROL
TRACK.  BECAUSE OF THE WIDE MODEL
SPREAD...THERE CONTINUES TO BE 
GREATER THAN USUAL TRACK FORECAST 
UNCERTAINTY.  

THROUGHOUT THE PERIOD...IT IS 
IMPORTANT NOT TO FOCUS ON THE EXACT
FORECAST TRACK DUE TO FORECAST 
UNCERTAINTIES AND THE FACT THAT
SIGNIFICANT HAZARDS EXTEND WELL 
AWAY FROM THE CENTER.

THE OFFICIAL FORECAST TRACK AND 
WIND RADII NECESSITATE THE ISSUANCE
OF A HURRICANE WARNING FOR THE 
NORTHERN GULF COAST AT THIS TIME. 

FORECAST POSITIONS AND MAX WINDS

INIT  26/2100Z 24.2N  82.3W   50 KT  60 MPH
 12H  27/0600Z 25.1N  83.9W   55 KT  65 MPH
 24H  27/1800Z 26.3N  85.9W   60 KT  70 MPH
 36H  28/0600Z 27.7N  87.6W   70 KT  80 MPH
 48H  28/1800Z 28.9N  88.5W   80 KT  90 MPH
 72H  29/1800Z 30.7N  89.5W   85 KT 100 MPH...INLAND
 96H  30/1800Z 32.5N  90.0W   30 KT  35 MPH...INLAND
120H  31/1800Z 34.5N  90.0W   20 KT  25 MPH...INLAND

$$
FORECASTER PASCH

T.S. Isaac Discussion #19 (25/2100 AUG UTC)

000
WTNT44 KNHC 252102
TCDAT4

TROPICAL STORM ISAAC DISCUSSION NUMBER  19
NWS NATIONAL HURRICANE CENTER MIAMI FL AL092012
500 PM EDT SAT AUG 25 2012

THE CENTER OF ISAAC IS CURRENTLY MOVING
ALONG THE NORTH COAST OF EASTERN CUBA.
THE SATELLITE APPEARANCE IS SOMEWHAT
DISORGANIZED... WITH THE MAIN CONVECTIVE
MASS 50 N MI OR MORE EAST OF THE LOW-LEVEL
CENTER.  AN AIR FORCE RESERVE HURRICANE
HUNTER AIRCRAFT HAS REPORTED 850 MB FLIGHT-
LEVEL WINDS OF 56 KT TO THE NORTHEAST OF
THE CENTER...WITH RELIABLE-LOOKING SFMR
SURFACE WIND DATA NEAR 50 KT. BASED ON 
THIS...THE INITIAL INTENSITY REMAINS 50 KT.
THE CENTRAL PRESSURE OF 997 MB IS BASED ON
A COMBINATION OF AIRCRAFT DATA AND
CUBAN SURFACE OBSERVATIONS.

THE INITIAL MOTION IS NOW 310/18.  
ISAAC IS CURRENTLY PART OF A LARGE 
LOW/MID-LEVEL LOW PRESSURE SYSTEM 
COVERING THE NORTHWESTERN CARIBBEAN SEA
AND THE ADJACENT LAND AND OCEAN AREAS.  
THIS LOW PRESSURE AREA HAS A SECOND 
VORTICITY CENTER BETWEEN JAMAICA AND 
THE CAYMAN ISLANDS...AND FOR THE NEXT 
24-36 HR ISAAC AND THIS CENTER WILL 
LIKELY ROTATE AROUND EACH OTHER.  
BASED ON THIS EXPECTATION... THE 
FORECAST TRACK SHOWS ISAAC MOVING
NORTHWESTWARD FOR 12 HR OR SO...
FOLLOWED BY A TURN TOWARD THE WEST-
NORTHWEST.  IT IS POSSIBLE THE STORM 
COULD MAKE A SHARPER TURN THAN FORECAST...
AS THE UKMET IS SHOWING AN ALMOST DUE WEST
MOTION BETWEEN THE FLORIDA KEYS AND CUBA
NEAR THE 36 HR POINT.  THE EARLY PART OF
THE FORECAST TRACK IS SHIFTED A LITTLE TO
THE LEFT OF THE PREVIOUS FORECAST...BUT 
STILL LIES TO THE RIGHT OF THE CONSENSUS
MODELS AND THE BULK OF THE DYNAMICAL
MODELS.  AFTER 36 HR...ISAAC SHOULD BREAK
FREE OF OR ABSORB THE REST OF THE LOW...
WITH THE SUBTROPICAL RIDGE TO THE EAST
BECOMING THE DOMINANT STEERING INFLUENCE.
THIS SHOULD ALLOW THE STORM TO GRADUALLY 
TURN TOWARD THE NORTHWEST AND NORTH OVER 
THE EASTERN AND NORTHERN GULF OF 
MEXICO...WITH AN EVENTUAL LANDFALL
ALONG THE NORTHERN GULF COAST IN 72-96
HR.  WHERE THIS MIGHT OCCUR IS STILL 
RATHER UNCERTAIN...WITH THE TRACK GUIDANCE
SPREAD BETWEEN SOUTHEASTERN LOUISIANA AND
THE CENTRAL FLORIDA PANHANDLE.  THIS PART
OF THE TRACK FORECAST LIES IN THE CENTER
OF THE GUIDANCE ENVELOPE NEAR THE 
CONSENSUS MODELS AND IS SIMILAR TO THE
PREVIOUS FORECAST.

A COMBINATION OF LIGHT WESTERLY VERTICAL
WIND SHEAR AND LAND INTERACTION SHOULD AT 
LEAST SLOW INTENSIFICATION FOR THE NEXT 12
HR.  AFTER THAT...THE SHEAR SHOULD DIMINISH 
WHILE THE CYCLONE REACHES OPEN WATER.  
THIS SHOULD ALLOW ISAAC TO GRADUALLY 
STRENGTHEN INTO A HURRICANE NEAR THE 
FLORIDA KEYS OR OVER THE SOUTHEASTERN GULF
OF MEXICO.  THE NEW INTENSITY FORECAST IS
SIMILAR TO THE PREVIOUS FORECAST AND IS
NEAR OR A LITTLE ABOVE THE INTENSITY
CONSENSUS.  IT SHOULD BE NOTED THAT THE 
GLOBAL MODELS ARE FORECASTING A VERY 
FAVORABLE PATTERN OF UPPER-LEVEL WINDS 
OVER THE NORTHERN GULF OF MEXICO BY 72 HR.
SHOULD THIS VERIFY AND SHOULD ISAAC 
ESTABLISH AN INNER CORE...THE CYCLONE 
COULD BE SIGNIFICANTLY STRONGER THAN
CURRENTLY FORECAST.

IT IS IMPORTANT NOT TO FOCUS ON THE 
EXACT TRACK OF ISAAC DUE TO THE
UNCERTAINTIES IN THE FORECAST AND THE
FACT THAT ISAAC HAS A LARGE AREA OF 
TROPICAL STORM FORCE WINDS ASSOCIATED WITH IT.


FORECAST POSITIONS AND MAX WINDS

INIT  25/2100Z 21.3N  76.0W   50 KT  60 MPH
 12H  26/0600Z 22.6N  78.0W   55 KT  65 MPH
 24H  26/1800Z 24.1N  80.6W   60 KT  70 MPH
 36H  27/0600Z 25.2N  82.7W   65 KT  75 MPH
 48H  27/1800Z 26.5N  84.3W   75 KT  85 MPH
 72H  28/1800Z 29.0N  86.0W   85 KT 100 MPH
 96H  29/1800Z 31.5N  86.0W   55 KT  65 MPH...INLAND
120H  30/1800Z 33.5N  85.5W   25 KT  30 MPH...INLAND

$$
FORECASTER BEVEN

Hurricane Irene Discussion #8

000
WTNT44 KNHC 221504
TCDAT4

HURRICANE IRENE DISCUSSION NUMBER 8
NWS NATIONAL HURRICANE CENTER MIAMI FL AL092011
1100 AM AST MON AUG 22 2011

DATA FROM A RECONNAISSANCE PLANE...RADAR AND SATELLITE IMAGERY INDICATE THAT IRENE HAS CONTINUED TO GRADUALLY BECOME BETTER ORGANIZED. HOWEVER THE WINDS WINDS HAVE NOT INCREASED SIGNIFICANTLY AND THE MINIMUM CENTRAL PRESSURE WAS AROUND 988 MB IN THE LAST CENTER DROPSONDE. THE INITIAL INTENSITY HAS BEEN INCREASED TO 70 KNOTS IN THIS ADVISORY. SINCE THE CORE OF THE HURRICANE IS NOT FORECAST TO MOVE DIRECTLY OVER THE HIGH TERRAIN OF HISPANIOLA...AND THE OCEANIC AND ATMOSPHERIC CONDITIONS ARE QUITE FAVORABLE... THE OFFICIAL FORECAST CALLS FOR INTENSIFICATION...AND MAKES IRENE A CATEGORY 3 HURRICANE AS IT MOVES ACROSS THE CENTRAL BAHAMAS. THIS IS CONSISTENT WITH MOST OF THE DYNAMICAL GUIDANCE AND IN FACT...EVEN GLOBAL MODELS FORECAST A SIGNIFICANT DROP IN THE CENTRAL PRESSURE OVER THE NEXT TWO OR THREE DAYS. IRENE IS BECOMING A LARGE CYCLONE...AND BASED ON BUOY OBSERVATIONS THE TROPICAL STORM FORCE WINDS EXTEND 160 N MI TO THE NORTHEAST OF THE CENTER.

RADAR AND RECONNAISSANCE FIXES INDICATE THAT THE HURRICANE IS MOVING TOWARD THE WEST-NORTHWEST OR 295 DEGREES AT ABOUT 12 KNOTS. IRENE IS CURRENTLY LOCATED SOUTH OF A NARROW SUBTROPICAL RIDGE WHICH IS FORCING THE CYCLONE ON A WEST-NORTHWEST TRACK. HOWEVER...MOST OF THE GLOBAL MODELS SHOW THE GRADUAL DEVELOPMENT A LARGE UPPER TROUGH ALONG THE UNITED STATES EAST COAST. THIS PATTERN WILL INDUCE A MORE NORTHWESTWARD AND THEN NORTHWARD TRACK THROUGH THE FORECAST PERIOD WITH A DECREASE IN FORWARD SPEED. BASED ON THE LATEST GUIDANCE... THE OFFICIAL TRACK FORECAST HAS BEEN SHIFTED TO THE EAST...BUT STILL REMAINS SLIGHTLY WEST OF THE MODEL CONSENSUS. ALTHOUGH IT IS TOO EARLY TO BE CERTAIN...THE CURRENT GUIDANCE LESSENS THE THREAT TO SOUTH FLORIDA.

DO NOT TO FOCUS ON THE EXACT FORECAST TRACK...ESPECIALLY AT DAYS 4 TO 5...SINCE THE MOST RECENT 5-YEAR AVERAGE ERRORS AT THOSE FORECAST TIMES ARE 200 AND 250 MILES...RESPECTIVELY.


FORECAST POSITIONS AND MAX WINDS

INIT 22/1500Z 19.2N 67.5W 70 KT 80 MPH
12H 23/0000Z 19.9N 69.2W 75 KT 85 MPH
24H 23/1200Z 20.5N 71.4W 80 KT 90 MPH
36H 24/0000Z 21.2N 73.2W 85 KT 100 MPH
48H 24/1200Z 22.0N 75.0W 90 KT 105 MPH
72H 25/1200Z 25.0N 77.5W 100 KT 115 MPH
96H 26/1200Z 28.5N 79.0W 100 KT 115 MPH
120H 27/1200Z 32.5N 80.0W 100 KT 115 MPH

$$
FORECASTER AVILA