Tropical Depression Isaac:

[ticka1]

where is the coc?

[unome]

where is the coc?

this video from Jim Williams at http://hurricanecity.com/ will show you

http://www.youtube.com/watch?v=nVYb4J-4 ... hMF0aN1Z9A

[srainhoutx]

where is the coc?

A closer inspection of the first HiRes rapid scan VIS Imagery suggest just NE of Guantanamo and it appears that a more WNW motion has started.

[srainhoutx]

06Z HWRF and GFDL:

[srainhoutx]

NCEP Operational Status Message
Sat Aug 25 13:32:03 2012 GMT
NOUS42 KWNO 251331
ADMNFD
SENIOR DUTY METEOROLOGIST NWS ADMINISTRATIVE MESSAGE
NWS NCEP CENTRAL OPERATIONS COLLEGE PARK MD
1330Z SAT AUG 25 2012
THE 12Z NAM BEGAN ON SCHD WITH GOOD US/CAN/CARIB UPA
DATA COVERAGE INCL 71 CONUS 14 AK 32 CAN AND 7 CARIB
RAOBS. NO MEX RAOBS WERE AVBL...SDM WILL CONTINUE TO
MONITOR FOR THESE. ALSO 24 DROPSONDE AND 4 700 MB FL
RECON REPORTS VCNTY TS ISAAC WERE AVBL. RAOB RECAP...
DVN.74455 - GROUND EQUIPMENT OUTAGE...CODE 10142.
PNI/91348 - GROUND EQUIPMENT OUTAGE...CODE 10142.
NKX/72293 - DELETED TEMPS 922-906 MB...WET-BULB EFFECT.
VBG/72393 - DELETED TEMPS 934-906 MB...WET-BULB EFFECT.
VPS/72221 - DEL HGTS 200 MB AND UP...HYDROSTATIC ERRORS.
CRITICAL WEATHER DAY STATUS...
CWD IS TO REMAIN IN EFFECT THRU THE COMING WEEK IN SUPPORT OF
MONITORING TS/HCN ISAAC AND POTENTIAL IMPACT ON SE US
AND IN SUPPORT OF THE REPUBLICAN NATL CONV IN TAMPA FL.
STOUDT/SDM/NCO/NCEP

[redneckweather]

IF Isaac somehow is able to get on over to Louisiana, then I am heading to him. I missed out on my severe weather chasing during the spring this year. Florida is too far but I think I can do La.

[biggerbyte]

Official forecast still has the same general areas to be initially effected. Still a few days out. As of today, anything west of NOLA is fine.

[TXStormjg]

Official forecast still has the same general areas to be initially effected. Still a few days out. As of today, anything west of NOLA is fine.

Do you think that could change or will be fine regardless...

[srainhoutx]

Official forecast still has the same general areas to be initially effected. Still a few days out. As of today, anything west of NOLA is fine.

Do you think that could change or will be fine regardless...

PRELIMINARY EXTENDED FORECAST DISCUSSION
NWS HYDROMETEOROLOGICAL PREDICTION CENTER COLLEGE PARK MD
956 AM EDT SAT AUG 25 2012

VALID 12Z WED AUG 29 2012 - 12Z SAT SEP 01 2012

OVER THE COURSE OF THE MEDIUM RANGE PERIOD THE LARGE SCALE FLOW IS
FCST TO TREND LESS AMPLIFIED WITH TIME... BY DAY 7 SAT YIELDING A
PRIMARY BAND OF WESTERLIES ACROSS MUCH OF SRN CANADA AND EXTENDING
ONLY INTO THE EXTREME NRN CONUS. 09Z NHC ADVISORY EXPECTS T.S.
ISAAC TO ACHIEVE HURCN STATUS OVER THE ERN GULF AND THEN MAKE
LANDFALL OVER THE FL PANHANDLE AROUND TUE NIGHT... REACHING
E-CNTRL AL WED NIGHT/EARLY THU. EXTRAPOLATION FROM THE NHC DAY 5
POSN MAINTAINS GOOD CONTINUITY WITH YDAYS NHC/HPC COORDINATED
TRACK INTO CNTRL TN/KY BY DAY 6 FRI. THIS MOTION IS CONTINUED NWD
FOR DAY 7... WITH FINAL ISSUANCE IN THE AFTN REFLECTING TODAYS 17Z
NHC/HPC COORDINATION. THE EXPECTED TREND TOWARD HAVING THE
WESTERLIES AT A FAIRLY NWD LATITUDE BY LATE IN THE PERIOD SHOULD
LEAD TO MODERATELY SLOW MOVEMENT OF ISAAC ONCE THE SYSTEM IS WELL
INLAND.

SPREAD PERSISTS WITH THE TIMING OF ENERGY EJECTING FROM THE TROF
OFF THE PAC NW COAST AS OF EARLY DAY 3 TUE. OVER RECENT DAYS
ECMWF/EC MEAN RUNS HAVE TENDED TO BE ON THE FAST SIDE OF THE
SPREAD WITH EJECTION OF LEADING ENERGY WHILE GFS/GEFS MEAN SOLNS
HAVE GENERALLY DEFINED THE SLOWER SIDE. THESE TIMING DIFFS ALOFT
TRANSLATE TO SIMILAR TIMING DIFFS FOR THE SFC SYSTEM CROSSING SRN
CANADA AND THE NRN TIER CONUS. MULTI-DAY ADJUSTMENTS SEEN IN THE
GUIDANCE SEEM TO FAVOR A COMPROMISE APPROACH UNTIL THERE IS BETTER
AGREEMENT. BEHIND THIS SYSTEM THERE IS REASONABLE AGREEMENT THAT
UPSTREAM ENERGY WILL SUPPORT A RESIDUAL MEAN TROF NEAR THE WEST
COAST INTO DAY 7 SAT... BUT WITH HIGHER HGTS THAN SEEN IN THE
INITIAL DAY 3 FEATURE.

COMPARED TO EVOLUTION UPSTREAM... GUIDANCE HAS COME INTO BETTER
AGREEMENT WITH THE TROF FCST TO CROSS ERN CANADA AND THE NERN
CONUS DURING DAYS 3-5 TUE-THU. THIS AGREEABLE SCENARIO WOULD HAVE
THE TROF EXITING JUST SOON ENOUGH TO HAVE RELATIVELY MINOR
INFLUENCE ON ISAAC. THE 00Z GEFS MEAN IS NOW THE ONLY SOLN
SUGGESTING FAST RECURVATURE OF ISAAC INTO THE ATLC. SOME GFS RUNS
FROM THE PAST COUPLE DAYS WERE ALSO SLOWER/MORE AMPLIFIED WITH THE
TROF ALOFT AND THUS FASTER WITH RECURVATURE. 00Z/06Z VERSIONS OF
THE GFS ARE EWD OF THE NHC TRACK AS OF EARLY DAY 5 THU BUT THEN
ADJUST CLOSE TO YDAYS NHC/HPC COORDINATED CONTINUITY THEREAFTER.
CONSULT LATEST NHC ADVISORIES/DISCUSSIONS FOR FURTHER INFO
REGARDING ISAAC.

BASE MAPS FOR DAYS 3-5 TUE-THU ARE DERIVED FROM A BLEND OF 00Z/06Z
GFS AND 00Z ECMWF/UKMET TO REFLECT THE DESIRED COMPROMISE FOR THE
SYSTEM EJECTING FROM NEAR THE WEST COAST AND CONSENSUS WITH THE
ERN NOAM TROF. THIS SOLN REQUIRES RELATIVELY MINOR ADJUSTMENTS TO
REFLECT THE OFFICIAL TRACK FOR ISAAC ESP ON DAYS 3-4. BY DAYS 6-7
GOOD AGREEMENT IN THE LARGE SCALE PATTERN BUT TYPICAL UNCERTAINTY
IN DETAILS FAVOR A GENERAL BLEND OF 00Z-06Z GFS/00Z ECMWF RUNS AND
THEIR RESPECTIVE 00Z ENSEMBLE MEANS.

RAUSCH

[Portastorm]

In essence, while impacts of Isaac west of New Orleans appear unlikely at this time ... there is enough uncertainty beyond Day 3 to warrant paying attention.

[srainhoutx]

TROPICAL STORM ISAAC DISCUSSION NUMBER 18
NWS NATIONAL HURRICANE CENTER MIAMI FL AL092012
1100 AM EDT SAT AUG 25 2012

ISAAC HAS BEEN SOMEWHAT DISRUPTED BY ITS PASSAGE ACROSS HAITI. THE
LAST REPORT FROM AN AIR FORCE RESERVE HURRICANE HUNTER AIRCRAFT
SHOWED THAT THE CENTER PRESSURE HAD RISEN TO 998 MB...AND THAT THE
STRONGEST FLIGHT-LEVEL WINDS WERE 60-70 N MI FROM THE CENTER. THESE
WINDS SUPPORT AN INITIAL INTENSITY OF 50 KT. THE CONVECTIVE
PATTERN IS DISORGANIZED...WITH LARGE CONVECTIVE BANDS SOUTH OF
HISPANIOLA AND LITTLE CONVECTION CURRENTLY NEAR THE CENTER. IT
SHOULD BE NOTED THAT ISAAC IS AT THE EASTERN END OF A LARGE AND
ELONGATED LOW PRESSURE SYSTEM OVER THE NORTHWESTERN CARIBBEAN
SEA...WHICH IS CREATING A LARGE AREA OF STRONG EASTERLY LOW-LEVEL
WINDS WELL TO THE NORTHWEST OF THE CENTER.

THE LOW-LEVEL CENTER HAS JOGGED WESTWARD DURING THE PAST FEW
HOURS...AND THE INITIAL MOTION IS A SOMEWHAT UNCERTAIN 315/15. IN
THE SHORT-TERM...A MID/UPPER-LEVEL TROUGH OVER THE EASTERN UNITED
STATES IS LIFTING OUT TO THE NORTHEAST AS A UPPER-LEVEL LOW MOVES
SOUTHWARD ACROSS THE CENTRAL GULF OF MEXICO. THIS EVOLUTION...
COMBINED WITH THE LOW-LEVEL RIDGE NORTH OF ISAAC...SHOULD STEER THE
CYCLONE GENERALLY NORTHWESTWARD NEAR THE NORTH COAST OF CUBA AND THE
FLORIDA KEYS DURING THE NEXT 48 HR AS INDICATED BY THE TIGHTLY-
CLUSTERED MODEL GUIDANCE. AFTER THAT...THE CYCLONE IS EXPECTED TO
MOVE AROUND THE WESTERN END OF THE SUBTROPICAL RIDGE AND TURN MORE
NORTHWARD OVER THE EASTERN GULF OF MEXICO. WHILE THE GUIDANCE
GENERALLY AGREES WITH THIS SCENARIO...THERE IS A SPREAD IN
POTENTIAL LANDFALL LOCATIONS BETWEEN THE EASTERN FLORIDA PANHANDLE
AND SOUTHEASTERN LOUISIANA...WHICH LOWERS CONFIDENCE IN THE FINAL
LANDFALL POINT. THE NEW FORECAST TRACK FOLLOWS THE CENTER OF THE
GUIDANCE ENVELOPE AND THE CONSENSUS MODELS IN CALLING FOR LANDFALL
IN THE WESTERN FLORIDA PANHANDLE BETWEEN 72-96 HR.

LITTLE CHANGE IN STRENGTH IS EXPECTED TODAY DUE TO A COMBINATION OF
LAND INTERACTION...SOME WESTERLY SHEAR...AND THE CURRENT LACK OF
CONVECTION. THE SHEAR IS FORECAST TO DECREASE AS THE CENTER MOVES
AWAY FROM LAND...WOULD SHOULD ALLOW FOR STRENGTHENING AFTER 12 HR.
THE NEW INTENSITY FORECAST IS SIMILAR TO THE PREVIOUS FORECAST
THROUGH 48 HR...THEN CALLS FOR A LITTLE MORE STRENGTHENING THAN THE
PREVIOUS FORECAST OVER THE NORTHERN GULF. THE CYCLONE SHOULD
WEAKEN TO A DEPRESSION AFTER LANDFALL ON THE NORTHERN GULF COAST.

THE NEW NHC FORECAST NECESSITATES THE ISSUANCE OF ADDITIONAL
TROPICAL STORM WARNINGS AND WATCHES FOR PORTIONS OF THE FLORIDA
PENINSULA.

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 25/1500Z 20.1N 74.6W 50 KT 60 MPH
12H 26/0000Z 21.7N 76.4W 50 KT 60 MPH
24H 26/1200Z 23.3N 79.0W 55 KT 65 MPH
36H 27/0000Z 24.7N 81.3W 65 KT 75 MPH
48H 27/1200Z 25.9N 83.1W 75 KT 85 MPH
72H 28/1200Z 28.5N 85.5W 85 KT 100 MPH
96H 29/1200Z 31.5N 86.5W 65 KT 75 MPH...INLAND
120H 30/1200Z 33.0N 86.0W 30 KT 35 MPH...INLAND

$$
FORECASTER BEVEN

[srainhoutx]

Morning Update from Jeff:

Hurricane Warnings are issued for the SW FL coast from Bonita, FL south to Key West.

Hurricane Watch is in effect for the SE FL coast from Golden Beach southward.

Tropical Storm Warning is in effect for the SE FL coast south of Jupiter Inlet including metro Miami.

Discussion:
After being close to hurricane intensity last evening, Isaac crossed over the SW tip of Haiti with a large part of the circulation going across the mountains of Hispaniola. This has disrupted the overall circulation and once again Isaac is looking poorly organized on satellite images. The center appears to be near the western edge of the deep convection and the upper level outflow which has been very good the past several days has become restricted on the western side due to a trough over the SE Gulf of Mexico into FL. Isaac has been moving toward the NW and is nearing the eastern part of Cuba.

Track:
Forecast models are in good agreement that the trough currently just west of Isaac will lift NE allowing the sub-tropical ridge to build westward over the next 24-36 hours turning the system from the current NW heading to a more WNW heading. How fast this happens will determine exactly where Isaac crosses the FL coast the first time. Based on the current motion and speed, Isaac should cross over eastern Cuba this afternoon and then move toward the FL Keys tonight and Sunday. Isaac will then enter into the SE Gulf of Mexico and begin to turn toward the NW and N as a ridge of high pressure over the central plains amplifies due to a short wave moving into the Pac NW. This increasing ridging will result in the digging of a downstream trough over the SE US which should pull Isaac northward. How quickly this happens and where Isaac is when he begins to make the N turn will determine the final landfall on the US Gulf coast.

Forecast models remain in decent agreement with a landfall from eastern MS to the FL panhandle with a good clustering over the west/central FL panhandle. While the CMC has shifted way west in its 00Z run, it is currently being discounted. The GFDL and HWRF have also shifted west overnight, but the GFS and ECMWF (the two best models) are nearly on top of each other into the FL panhandle and the GFS has been extremely consistent. On this track Isaac will be approaching the US Gulf coast late Tuesday.

NOTE: it is important to understand that this is an above average size storm with Tropical Storm force winds extending outward 230 miles from the center. Adverse conditions will arrive well before the center and extend well away from the center.

Intensity:
While Isaac is not spending much time of the land areas of the Caribbean Islands, the inner core does appear to be somewhat disrupted this morning. With that said, the slight NE trend in the forecast track in the short term suggest Isaac will be firmly back over the warm waters of the FL Straits and the interaction with Cuba will be short. The upper levels currently do not look as favorable as they were forecast to be with the trough to the west restricting outflow and maybe even imparting a little bit of shear. This trough will lift out today and conditions should improve, but Isaac has a very large circulation and it will take time for the system to intensify. With that said, most of the guidance brings the system to hurricane intensity has in move into the FL Keys and then maintain category 1/low end category 2 intensity to landfall on the Gulf coast. The latest HRWF takes Isaac to a strong category 3 hurricane, but this is being discounted currently. Over the Gulf of Mexico Isaac will be crossing warm water, but the best heat potential (energy) is located over the central and western Gulf and not along the track of the system.

Impacts:
Preparations to protect life and property should be rushed to completion in the hurricane warning area. Storm surge values of 5-8 feet will be possible along the SW FL coast south of Cape Coral where strong south winds will pile the sea water against the SE/NE angle of the coast. Values may be locally higher in small inlets and bays. Near the final landfall location, some significant storm surge will be possible into Apalachicola Bay similar to Hurricane Dennis in 2005. Rainfall amounts of 5-10 inches will be possible across S FL spreading north across much of FL Sun-Tues. Hurricane conditions are likely over the FL Keys late Sunday and then spreading up the SW FL coast into Monday. Hurricane conditions will begin to impact the northern Gulf coast by midday Tuesday.

NHC forecast Track and Error Cone:

[srainhoutx]

12Z GFS suggest a tad further W:

[srainhoutx]

12Z GFS nearing the MS/AL Border:

[sambucol]

So, there is some uncertainty once Isaac enters the GOM regarding a more west track?

[srainhoutx]

So, there is some uncertainty once Isaac enters the GOM regarding a more west track?

It has trended toward the Euro solution and as the NHC and HPC have pointed out, the forecast beyond day 2-3 is not a clear cut forecast and a lot of uncertainty remains.

[wxman57]

So, there is some uncertainty once Isaac enters the GOM regarding a more west track?

Of course there's uncertainty. I researched landfall projections along the northern Gulf Coast over the past 10 years and found that the typical projection of the landfall point 72 hours out was about 110 miles. That error drops to about 70 miles at 48 hrs out and 40-45 miles 24 hours out.

[Scott747]

In essence, while impacts of Isaac west of New Orleans appear unlikely at this time ... there is enough uncertainty beyond Day 3 to warrant paying attention.

Agree. It's way too early to proclaim anything W of Nola as being fine.

I mentioned last night there was the interesting movement after landfall turning the system back towards the W/WNW after initially shunting off to the NE.

12z GFS is W somewhat with a heading in the Gulf that should get anyone's attention in Louisiana.

[sambucol]

All agree on high pressure holding firm over Texas next week with another center east of the U.S. Coast. Weakness is between SE LA and the eastern FL Panhandle. My initial estimate of the western FL Panhandle for final landfall looks good for now. Don't see any threat to Houston.

Wxman57, do you still agree that the high pressure will hold firm over Texas and that you still don't see any threat to Houston?

[Scott747]

Per usual many of us get caught up looking at long range models and tend to overlook real time obs.

Isaac isn't the healthiest looking system at the moment. Interaction with Haiti and Eastern Cuba has taken a toll where it looked for a time last night it was going to retain much of its organization.