Tropical Storm Irwin at EPAC

[cycloneye]

TCDEP4
TROPICAL DEPRESSION NINE-E DISCUSSION NUMBER 2
NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL
8 PM PDT THU AUG 25 2005

THE OVERALL APPEARANCE OF T.D. NINE HAS NOT IMPROVED THIS EVENING
AND THE SYSTEM IS ENCOUNTERING NORTHEASTERLY SHEAR. DVORAK T NUMBERS
FROM TAFB AND SAB ARE A CONSENSUS 2.0 OR 30 KT...WHICH WILL BE THE
INITIAL INTENSITY FOR THIS ADVISORY. THE FORECAST INTENSITY IS VERY
CLOSE TO THE SHIPS GUIDANCE WHICH INDICATES A LESSENING OF THE
SHEAR WITHIN 12-18 HOURS WHILE THE CYCLONE TRAVERSES WARM SSTS.
BY 48 HOURS...THE CYCLONE WILL BE PASSING OVER THE COLD WAKE OF
HURRICANE HILARY. CONSEQUENTLY...MODEST INTENSIFICATION IS BEING
FORECAST UNTIL THAT TIME. BEYOND THAT TIME...THE CYCLONE SHOULD BE
MOVING OVER CLIMATOLOGICALLY COOLER WATERS WITH DISSIPATION
EXPECTED BY 120 HOURS.

THE INITIAL MOTION REMAINS 280/10. THE DEPRESSION IS SOUTH OF A
MID-LEVEL RIDGE THAT IS FORECAST TO BUILD WESTWARD OVER THE NEXT
FEW DAYS...AND THIS SHOULD KEEP THE SYSTEM ON A WEST TO WEST-
NORTHWESTWARD TRACK. THE OFFICIAL FORECAST IS ESSENTIALLY AN UPDATE
OF THE PREVIOUS AND CLOSE TO THE MEDIUM BAM GUIDANCE.

FORECASTER COBB/AVILA


FORECAST POSITIONS AND MAX WINDS

INITIAL 26/0300Z 17.2N 107.3W 30 KT
12HR VT 26/1200Z 17.5N 108.9W 35 KT
24HR VT 27/0000Z 17.9N 111.0W 45 KT
36HR VT 27/1200Z 18.2N 113.0W 50 KT
48HR VT 28/0000Z 18.5N 115.0W 55 KT
72HR VT 29/0000Z 19.0N 118.5W 50 KT
96HR VT 30/0000Z 19.5N 122.0W 40 KT
120HR VT 31/0000Z 19.5N 126.0W 30 KT...DISSIPATING

[cycloneye]

000
WTPZ44 KNHC 260834
TCDEP4
TROPICAL STORM IRWIN DISCUSSION NUMBER 3
NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL
2 AM PDT FRI AUG 26 2005

LATEST GOES-10 AND GOES-12 SATELLITE IMAGERY AND A 0518Z AMSU PASS
INDICATE THE CIRCULATION CENTER VERY CLOSE TO THE DEEP CONVECTION.
BASED ON DVORAK T NUMBERS OF 2.5 OR 35 KT FROM BOTH TAFB AND SAB
AND UNCONTAMINATED 35-40 KT WINDS FROM A 01Z QUIKSCAT PASS...T.D.
NINE HAS BEEN UPGRADED TO TROPICAL STORM IRWIN. CURRENTLY THE STORM
IS ENCOUNTERING NORTHEASTERLY SHEAR BUT THIS SHEAR IS FORECAST TO
RELAX A BIT IN THE NEXT 24-36 HOURS...PERHAPS ALLOWING IRWIN TO
INTENSIFY TO A 50 KT STORM IN 36 HOURS. THE OFFICIAL INTENSITY
FORECAST FOLLOWS CLOSELY WITH THE SHIPS GUIDANCE HOWEVER HOLDS
IRWIN TO 50 KT BASED ON THE LOCATION OF THE FORECAST TRACK RELATIVE
TO THE 26 DEGREE CELSIUS ISOTHERM. BEYOND TWO DAYS...THE CYCLONE
SHOULD MOVE OVER COOLER WATERS WITH DISSIPATION STILL EXPECTED IN
120 HOURS.

THE INITIAL MOTION REMAINS 280/10. IRWIN IS SOUTH OF A MID-LEVEL
RIDGE THAT IS FORECAST TO BUILD WESTWARD OVER THE NEXT FEW DAYS...
AND THIS SHOULD KEEP THE SYSTEM ON AN OVERALL WESTERLY TRACK. THE
GFDL...UKMET...AND NOGAPS MODELS DISSIPATE IRWIN IN TWO TO THREE
DAYS WHILE THE GFS MAINTAINS A CIRCULATION AND FORECASTS THE STORM
TO MOVE TO THE WEST-SOUTHWEST THROUGH FIVE DAYS. THE OFFICIAL
FORECAST IS A BLEND OF THE PREVIOUS FORECAST AND THE GFS GUIDANCE.

FORECASTER MAINELLI/KNABB


FORECAST POSITIONS AND MAX WINDS

INITIAL 26/0900Z 17.5N 108.2W 35 KT
12HR VT 26/1800Z 17.8N 109.6W 40 KT
24HR VT 27/0600Z 18.0N 111.6W 45 KT
36HR VT 27/1800Z 18.2N 113.6W 50 KT
48HR VT 28/0600Z 18.3N 115.5W 50 KT
72HR VT 29/0600Z 18.2N 119.1W 45 KT
96HR VT 30/0600Z 18.0N 123.0W 40 KT
120HR VT 31/0600Z 18.0N 126.0W 30 KT...DISSIPATING

[cycloneye]

TCDEP4
TROPICAL STORM IRWIN DISCUSSION NUMBER 4
NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL
8 AM PDT FRI AUG 26 2005

LATEST ENHANCED INFRARED IMAGERY DEPICT IRWIN AS A STRONGER TROPICAL
STORM. CONVECTION REMAINS SOUTH OF THE CENTER AS NORTHEASTERLY
SHEAR IMPACTS THE SYSTEM. THE INITIAL INTENSITY FOR IRWIN IS
INCREASED TO 45 KT BASED ON DVORAK ESTIMATES OF 3.0 FROM TAFB AND
SAB...THE UW-CIMSS OBJECTIVE DVORAK TECHNIQUE YIELDS 47 KT.

THE INTENSITY FORECAST CALLS FOR IRWIN TO REMAIN A TROPICAL STORM
OVER THE NEXT SEVERAL DAYS. IRWIN IS FORECAST TO REMAIN IN AN
ENVIRONMENT OF RELATIVELY WARM OCEAN WATERS AND MODERATE SHEAR
WHICH SHOULD ALLOW STRENGTHENING UP TO 50 KT. IN THE EXTENDED
FORECAST PERIOD...THE SHEAR INCREASES AND IRWIN CROSSES BEYOND THE
26 SST DEGREE ISOTHERM SO A DECREASE IN INTENSITY TO DEPRESSION
STRENGTH IS FORECAST.

THE INITIAL MOTION REMAINS 280/10. IRWIN IS EXPECTED TO REMAIN
SOUTH OF A MID-LEVEL RIDGE. THIS RIDGE IS FORECAST TO BUILD
WESTWARD KEEPING IRWIN ON A GENERALLY WESTWARD TRACK OVER THE NEXT
SEVERAL DAYS. THE OFFICIAL FORECAST TRACK FOLLOWS THE CONSENSUS
MODELS OUT TO 72 HRS. BEYOND 72 HOURS...THE FORECAST TRACK IS A
BLEND OF THE FSSE AND GFS TRACKS THAT KEEP IRWIN TRACKING WESTWARD.
THE CONSENSUS MODELS AND GFDL IN THE LATE PERIOD TRACK IRWIN ON A
NORTHWARD TRACK. THE OFFICIAL TRACK FORECAST CALLS FOR CONTINUED
WESTWARD MOTION ALONG THE SOUTHERN EXTENT OF THE MID-LEVEL RIDGE.

FORECASTER SISKO/STEWART


FORECAST POSITIONS AND MAX WINDS

INITIAL 26/1500Z 17.8N 109.2W 45 KT
12HR VT 27/0000Z 18.0N 110.7W 45 KT
24HR VT 27/1200Z 18.1N 112.6W 50 KT
36HR VT 28/0000Z 18.3N 114.6W 50 KT
48HR VT 28/1200Z 18.3N 116.4W 50 KT
72HR VT 29/1200Z 18.2N 120.1W 50 KT
96HR VT 30/1200Z 18.0N 123.5W 40 KT
120HR VT 31/1200Z 17.5N 126.5W 30 KT...DISSIPATING

[cycloneye]

WTPZ24 KNHC 262034
TCMEP4
TROPICAL STORM IRWIN FORECAST/ADVISORY NUMBER 5
NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL EP092005
2100Z FRI AUG 26 2005

TROPICAL STORM CENTER LOCATED NEAR 17.7N 110.1W AT 26/2100Z
POSITION ACCURATE WITHIN 20 NM

PRESENT MOVEMENT TOWARD THE WEST OR 280 DEGREES AT 10 KT

ESTIMATED MINIMUM CENTRAL PRESSURE 1000 MB
MAX SUSTAINED WINDS 45 KT WITH GUSTS TO 55 KT.
34 KT....... 40NE 60SE 60SW 40NW.
12 FT SEAS.. 60NE 60SE 60SW 60NW.
WINDS AND SEAS VARY GREATLY IN EACH QUADRANT. RADII IN NAUTICAL
MILES ARE THE LARGEST RADII EXPECTED ANYWHERE IN THAT QUADRANT.

REPEAT...CENTER LOCATED NEAR 17.7N 110.1W AT 26/2100Z
AT 26/1800Z CENTER WAS LOCATED NEAR 17.6N 109.6W

FORECAST VALID 27/0600Z 17.8N 111.5W
MAX WIND 45 KT...GUSTS 55 KT.
34 KT... 40NE 60SE 60SW 40NW.

FORECAST VALID 27/1800Z 17.9N 113.5W
MAX WIND 45 KT...GUSTS 55 KT.
34 KT... 60NE 60SE 60SW 60NW.

FORECAST VALID 28/0600Z 18.0N 115.4W
MAX WIND 45 KT...GUSTS 55 KT.
34 KT... 60NE 60SE 60SW 60NW.

FORECAST VALID 28/1800Z 18.0N 117.2W
MAX WIND 45 KT...GUSTS 55 KT.
34 KT... 60NE 60SE 60SW 60NW.

FORECAST VALID 29/1800Z 17.5N 121.0W
MAX WIND 40 KT...GUSTS 50 KT.
34 KT... 50NE 50SE 50SW 50NW.

EXTENDED OUTLOOK. NOTE...ERRORS FOR TRACK HAVE AVERAGED NEAR 200 NM
ON DAY 4 AND 250 NM ON DAY 5...AND FOR INTENSITY NEAR 20 KT EACH DAY

OUTLOOK VALID 30/1800Z 17.0N 124.0W
MAX WIND 35 KT...GUSTS 45 KT.

OUTLOOK VALID 31/1800Z 16.5N 127.0W...DISSIPATING
MAX WIND 30 KT...GUSTS 40 KT.

REQUEST FOR 3 HOURLY SHIP REPORTS WITHIN 300 MILES OF 17.7N 110.1W

NEXT ADVISORY AT 27/0300Z

FORECASTER SISKO/STEWART

[cycloneye]

TCDEP4
TROPICAL STORM IRWIN DISCUSSION NUMBER 5
NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL
2 PM PDT FRI AUG 26 2005

GOES-10 VISIBLE IMAGERY OF IRWIN SHOWS NORTHEASTERLY SHEAR CONTINUES
TO IMPACT THE TROPICAL CYCLONE AS THE MAIN CONVECTION IS CONFINED
TO THE SOUTHWEST QUADRANT AND THE CENTER IS NOW PARTIALLY EXPOSED.
DVORAK ESTIMATES FROM TAFB AND SAB REMAIN AT 3.0 OR 45 KT.
SIMILARILY...THE MOST RECENT UW-CIMSS AND CSU-CIRA AMSU MICROWAVE
INTENSITY ESTIMATES ARE ALSO AROUND 45 KT. BASED ON THESE PRESENT
INTENSITY ESTIMATES...THE INITIAL OFFICIAL INTENSITY REMAINS AT 45
KT FOR THIS ADVISORY.

THE INTENSITY FORECAST KEEPS IRWIN AS A TROPICAL STORM FOR THE NEXT
SEVERAL DAYS. THE GFDL AND FSSE INTENSITY MODELS KEEP THE SYSTEM
BELOW 50 KT AND THEN WEAKEN IT TO DEPRESSION STRENGTH BEYOND 72
HRS. THE SHIPS MODEL PREDICTS IRWIN WILL REACH 50 KT IN THE 24-48
HR FORECAST PERIOD AND THEN FOLLOWS A SIMILAR TREND AS THE GFDL AND
FSSE. THE OFFICIAL INTENSITY FORECAST IS A BLEND OF THE AVAILABLE
INTENSITY GUIDANCE AND IT CAPS THE INTENSITY AT 45 KT IN THE FIRST
72 HRS AND EVENTUALLY DROPS IRWIN TO A TROPICAL DEPRESSION IN THE
LATER PERIOD. IF THE SHEAR CONTINUES TO IMPACT IRWIN OVER THE NEXT
DAY...THEN FASTER WEAKENING IS LIKELY.

THE INITIAL MOTION REMAINS 280/10. THERE IS LITTLE CHANGE IN
FORECAST TRACK FROM THE PREVIOUS. IRWIN WILL REMAIN SOUTH OF A
MID-LEVEL RIDGE AND IT WILL CONTINUE TO MOVE WESTWARD OVER THE NEXT
SEVERAL DAYS. THIS SCENARIO IS CONSISTENT WITH MOST OF THE
INDIVIDUAL MODELS AND CONSENSUS MODELS. IN THE EXTENDED RANGE...THE
FORECAST FOLLOWS THE NOGAPS AND GFS WEST-SOUTHWESTWARD TRACKS.

FORECASTER SISKO/STEWART


FORECAST POSITIONS AND MAX WINDS

INITIAL 26/2100Z 17.7N 110.1W 45 KT
12HR VT 27/0600Z 17.8N 111.5W 45 KT
24HR VT 27/1800Z 17.9N 113.5W 45 KT
36HR VT 28/0600Z 18.0N 115.4W 45 KT
48HR VT 28/1800Z 18.0N 117.2W 45 KT
72HR VT 29/1800Z 17.5N 121.0W 40 KT
96HR VT 30/1800Z 17.0N 124.0W 35 KT
120HR VT 31/1800Z 16.5N 127.0W 30 KT...DISSIPATING