Tropical Storm Isaac, Part 2: Isaac Moving Into The Gulf Of Mexico-Hurricane Warnings For Morgan City, LA/MS/AL & FL Panhandle To Destin, FL

[Superstorm93]

Despite the center fixes, they put the center at 17.3N 72.0W in the new advisory. Is this just a continuity value? It's really more like 17.0N 72.0W.

Meh, I'm not surprised. They have been taking continuity values for this system since it entered the Caribbean.

The 6 hour average might be WNW (or even NW), but this has slowed down significantly over the past few hours.

[phil882]

Time for some GFS Verifications agains the G-IV data that has been rolling in.

Position: 27N 79W (Near E Florida Coast)

G-IV - 5880 meters

GFS 12z - 5873 meters (7 m too weak)

GFS 18z - 5872 meters (8 m too weak)

Position: 25N 74W (Far NW of Isaac)

G-IV - 5880 meters

GFS 12z - 5873 meters (7 m too weak)

GFS 18z - 5876 meters (4 m too weak)

Position: 21.5N 71.5W (N of Isaac)

G-IV - 5860 meters

GFS 12z - 5856 meters (4 m too weak)

GFS 18z - 5858 meters (2 m too weak)

Position: 21N 74N (NW of Isaac)

G-IV - 5850 meters

GFS 12z - 5851 meters (1 m too strong)

GFS 18z - 5840 meters (1 m too weak)

Generally the soundings indicate the GFS was little bit too weak with the mid-level ridging for both the 12z and 18z runs, with the 18z run being a little bit closer to reality. It will interesting to see how these obs will affect the track of Isaac in subsequent runs.

[Camille>Katrina]

So Phil these ahe High pressure heights(?) and the info is telling the it's alittle stronger than anticipated correct?I am assuming that but are these that far off to affect model output?Then if it just got sampled yesterday and these are enough to matter why the delineation so quickly from 24hrs ago?

Thanks Phil so it was possibily enough to kick it W some,interesting.

[HurricaneJosh]

Generally the soundings indicate the GFS was little bit too weak with the mid-level ridging for both the 12z and 18z runs, with the 18z run being a little bit closer to reality. It will interesting to see how these obs will affect the track of Isaac in subsequent runs.

So, then, the further-W solution seen in the 18Z might actually be reality-based? Curious now to see the 00Z. (Well... Of course I was already curious to see it...)

[Sunny and Warm]

Time for some GFS Verifications agains the G-IV data that has been rolling in.

Generally the soundings indicate the GFS was little bit too weak with the mid-level ridging for both the 12z and 18z runs, with the 18z run being a little bit closer to reality. It will interesting to see how these obs will affect the track of Isaac in subsequent runs.

Which is why the 18z bent Isaac a little further west with time than the 12z did I would hazard. The first 72 hours is heavily influenced by the trough, and I'd like to know how the incoming data on that trough is compared to both the 12z and 18z runs.

[wxmx]

Latest fix will probably be very close to the advisories initial position, as recon found there the wind shift 17.3N 72W... 993mb

[Connor McCrorey]

I can't be the only one who thinks NHC is still a bit north of the actual center, can I? I understand using the coordinates they're using for continuity, but I still think the true center has finally organized just a tad south/west of the official location. Even the latest sonde dropped in the "eye" (993 mb) was a bit SW of the official position. Maybe not by much, but every mile to the left is another mile away from the mountains. The GFS underestimating the ridge strength I find very telling. 7-8 meters is a significant enough difference in height, in my opinion, to warrant at least a few question marks regarding how well the model is handling the track, especially a few days down the road. I think it will be Sunday or so before we can really assess the track and intensity forecast with much confidence (aka enough to book flights, @Josh/myself/others interested in chasing Isaac), but I'm banking pretty heavily on Isaac missing/just brushing Hispanola and remaining organized enough to strengthen fairly rapidly upon emergence over the Gulf.

[wxsouth]

Time for some GFS Verifications agains the G-IV data that has been rolling in.

Position: 27N 79W (Near E Florida Coast)

G-IV - 5880 meters

GFS 12z - 5873 meters (7 m too weak)

GFS 18z - 5872 meters (8 m too weak)

Position: 25N 74W (Far NW of Isaac)

G-IV - 5880 meters

GFS 12z - 5873 meters (7 m too weak)

GFS 18z - 5876 meters (4 m too weak)

Position: 21.5N 71.5W (N of Isaac)

G-IV - 5860 meters

GFS 12z - 5856 meters (4 m too weak)

GFS 18z - 5858 meters (2 m too weak)

Position: 21N 74N (NW of Isaac)

G-IV - 5850 meters

GFS 12z - 5851 meters (1 m too strong)

GFS 18z - 5840 meters (1 m too weak)

Generally the soundings indicate the GFS was little bit too weak with the mid-level ridging for both the 12z and 18z runs, with the 18z run being a little bit closer to reality. It will interesting to see how these obs will affect the track of Isaac in subsequent runs.

Little bit of caution here. The dropsondes are returning values to the nearest 10 meters, so most of those comparisons are within the rounding error of the sonde. Overall, the obs match the model quite well.

[wxmx]

Latest

Product: Air Force Vortex Message (URNT12 KNHC)

Transmitted: 25th day of the month at 01:08Z

Aircraft: Air Force Aircraft (Last 3 digits of the tail number are 300)

Storm Number & Year: 09L in 2012

Storm Name: Isaac (flight in the North Atlantic basin)

Mission Number: 12

Observation Number: 22

A. Time of Center Fix: 25th day of the month at 0:12:20Z

B. Center Fix Coordinates: 17°16'N 72°03'W (17.2667N 72.05W)

B. Center Fix Location: 90 miles (145 km) to the SSE (168°) from Port-au-Prince, Haiti.

C. Minimum Height at Standard Level: 1,372m (4,501ft) at 850mb

D. Estimated (by SFMR or visually) Maximum Surface Wind: 58kts (~ 66.7mph)

E. Location of the Estimated Maximum Surface Wind: 19 nautical miles (22 statute miles) to the SSW (197°) of center fix

F. Maximum Flight Level Wind Inbound: From 302° at 53kts (From the WNW at ~ 61.0mph)

G. Location of Maximum Flight Level Wind Inbound: 33 nautical miles (38 statute miles) to the SW (234°) of center fix

H. Minimum Sea Level Pressure: 994mb (29.35 inHg) - Extrapolated

I. Maximum Flight Level Temp & Pressure Altitude Outside Eye: 14°C (57°F) at a pressure alt. of 1,524m (5,000ft)

J. Maximum Flight Level Temp & Pressure Altitude Inside Eye: 19°C (66°F) at a pressure alt. of 1,525m (5,003ft)

K. Dewpoint Temp (collected at same location as temp inside eye): 19°C (66°F)

K. Sea Surface Temp (collected at same location as temp inside eye): Not Available

L. Eye Character: Not Available

M. Eye Shape: Not Available

N. Fix Determined By: Penetration, Wind, Pressure and Temperature

N. Fix Levels (sfc and flt lvl centers are within 5nm of each other): Surface and 850mb

O. Navigation Fix Accuracy: 0.02 nautical miles

O. Meteorological Accuracy: 1 nautical mile

Remarks Section - Remarks That Were Decoded...

Maximum Flight Level Wind: 64kts (~ 73.6mph) in the east quadrant at 21:41:30Z

Sea Level Pressure Extrapolation From: 850mb

Remarks Section - Additional Remarks...

PRELIMINARY, DO NOT RETRANSMIT

[battlebrick]

Latest

dropsonde showed 993 with 10kts of wind....

[MGorse]

The wind really gusting in Barahona, Dominican Republic:

MDBH 250000Z 13025G50KT 090V180 2000 RA FEW010 BKN012 OVC070 23/23 Q1006 CB/NE/E/SE/S/NW

MDBH 242300Z 09026G52KT 3000 +RA FEW010CB BKN012 OVC070 23/23 Q1006 CB/ALL QDS

MDBH 242220Z 09025G50KT 4000 RA FEW010CB BKN012 OVC070 XX/XX Q1006 CB/NE/E/SE/S/NW/N

[SnowGoose69]

The wind really gusting in Barahona, Dominican Republic:

MDBH 250000Z 13025G50KT 090V180 2000 RA FEW010 BKN012 OVC070 23/23 Q1006 CB/NE/E/SE/S/NW

MDBH 242300Z 09026G52KT 3000 +RA FEW010CB BKN012 OVC070 23/23 Q1006 CB/ALL QDS

MDBH 242220Z 09025G50KT 4000 RA FEW010CB BKN012 OVC070 XX/XX Q1006 CB/NE/E/SE/S/NW/N

Thats probably strong enough to destroy 85% of the structures in that country.

[tmagan]

00Z Observations

[MGorse]

Thats probably strong enough to destroy 85% of the structures in that country.

Yeah probably...sadly enough.

[Windspeed]

Without a doubt, subsidence is occurring in the core. Check out rapid scan...

http://www.meteo.psu...D/anim16ir.html

Chances of this reaching hurricane intensity prior to landfall are certainly increasing based on the obvious slowdown and organizational changes in the past few hours.

[mahk_webstah]

perfect slot track over Western Haiti and eastern tip of Cuba into the straits with minimal disruption? Looks like a possibility.

[Superstorm93]

Inner core has really tightened up over the past 3 hours.

Wouldn't be surprised if recon found this to be 5-10 knots stronger by the time they arrive (If this is still over water)

One thing I am concerned about is how tight and compact this has become. The outer structure is still large, which may be the only thing that saves this.

Fun Fact: 00z TVCN would be the jackpot for this system. Maybe an hour or two over the fork of Hispaniola and minimal interaction with eastern Cuba. Thereafter it moves WNW just North of the Cuban coast and through the straights.

[Hurriplane]

Recon shows wind speeds have not changed.

Probably will remain the same as it was on the 5pm advisory.

[Camille>Katrina]

Cloud presentation says atleast for the short term movement will continue on a WNW -NW and as has been noted by a few here not much time over land;the shortest route possible Maybe.

[gkrangers]

Latest

19-14 spread. Finally.

[jhamps10]

NHC 11pm advisory 17.7N 72.5W Winds 70 MPH, movement NW at 14MPH

[Hurriplane]

70 mph winds moving at 14 due NW as of 11.

The cone also shifted back west by an inch.

[Superstorm93]

A HURRICANE WATCH AND A TROPICAL STORM WARNING HAVE BEEN ISSUED FOR

ALL OF THE FLORIDA KEYS...INCLUDING FLORIDA BAY...AND FOR THE COAST

OF THE SOUTHERN FLORIDA PENINSULA FROM OCEAN REEF ON THE EAST COAST

WESTWARD TO BONITA BEACH ON THE WEST COAST.

[HurricaneJosh]

The D4 position is near Fort Walton Beach with winds of 80 kt. Slight improvement.

[yoda]

The D4 position is near Fort Walton Beach with winds of 80 kt. Slight improvement.

Looks like majority of landfall would be overnight Tuesday into early Wednesday morning...

[wxsmwhrms]

Cloud presentation says atleast for the short term movement will continue on a WNW -NW and as has been noted by a few here not much time over land;the shortest route possible Maybe.

Last recon fixes where like 300, but it does like on the satellite there might have been a right wobble, likely associated with convection becoming better concentrated in the northeast quadrant and continued development of the inner core.

[yoda]

Finally here it is...

TROPICAL STORM ISAAC DISCUSSION NUMBER 16

NWS NATIONAL HURRICANE CENTER MIAMI FL AL092012

1100 PM EDT FRI AUG 24 2012

SATELLITE IMAGERY AND RECONNAISSANCE AIRCRAFT DATA INDICATE THAT THE

CIRCULATION AND CONVECTIVE ORGANIZATION OF ISAAC HAS CONTINUED TO

IMPROVE SINCE THE PREVIOUS ADVISORY. INFRARED AND MICROWAVE

SATELLITE IMAGERY SUGGEST THAT AN EYE IS FORMING...AND THIS IS THE

BASIS FOR INCREASING THE INTENSITY TO 60 KT.

THE INITIAL MOTION ESTIMATE IS 315/12 BASED ON RECON AND MICROWAVE

FIXES. ALTHOUGH THE TRACK FORCAST WAS ADJUSTED SLIGHTLY TO THE

RIGHT THROUGH 48 HOURS...NO OTHER SIGNIFICANT CHANGES WERE MADE TO

THE PREVIOUS ADVISORY TRACK. RECENT UPPER-AIR DATA AND NOAA G-IV

AIRCRAFT DROPSONDE DATA INDICATE THE TROUGH THAT HAS CREATED THE

BREAK IN THE SUBTROPICAL RIDGE ACROSS FLORIDA HAS SHIFTED TO A

POSITION JUST EAST OF THE FLORIDA PENINSULA. THE 18Z GFS MODEL...

WHICH SHIFTED TO THE RIGHT OF ITS 12Z TRACK...CAPTURED THIS FARTHER

EAST POSITION...WHEREAS THE 18Z UKMET AND 12Z ECMWF KEPT THE TROUGH

ACROSS THE WESTERN FLORIDA PENINSULA VALID AT 00Z THIS EVENING.

BASED ON THE GFS VERIFYING BETTER THAN THE OTHER MODELS AT 00Z THIS

EVENING...THE NHC TRACK HAS BEEN SHIFTED A LITTLE TO THE RIGHT.

AFTER 48 HOURS...THE RIDGE IS EXPECTED TO BUILD BACK WESTWARD

ACROSS FLORIDA AND KEEPING ISAAC ON A MOSTLY NORTHWESTWARD HEADING

ACROSS THE EASTERN AND NORTH-CENTRAL GULF MEXICO. THE OFFICIAL

FORECAST TRACK IS CLOSE TO THE CONSENSUS MODELS TVCA AND TV15

THROUGH 48 HOURS...AND THEN IS A LITTLE TO THE RIGHT OF THOSE

MODELS AFTER THAT.

WITH THE INNER CORE CONVECTION IMPROVING...THERE IS STILL THE

POSSIBILITY THAT ISAAC COULD REACH HURRICANE INTENSITY BEFORE

REACHING HAITI TONIGHT. THE INTENSITY FROM 12-24 HOURS WILL BE

DETERMINED BY THE AMOUNT OF LAND INTERACTION WITH HAITI AND EASTERN

CUBA. AFTER THAT...THE SLIGHT EASTWARD SHIFT IN THE FORECAST TRACK

IS ENOUGH TO PLACE ISAAC OVER WATER LONGER THAN WHAT WAS INDICATED

IN THE PREVIOUS INTENSITY FORECAST REQUIRED AN INCREASE IN THE

INTENSITY FORECAST. THE EASTWARD TRACK SHIFT AND A LARGER INITIAL

AND FORECAST WIND FIELD TO THE NORTH ARE WHAT NECESSITATED THE

CHANGES IN THE WATCHES AND WARNINGS FOR FLORIDA.

IT IS IMPORTANT NOT TO FOCUS ON THE EXACT TRACK 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 25/0300Z 17.7N 72.5W 60 KT 70 MPH

12H 25/1200Z 19.4N 74.1W 50 KT 60 MPH

24H 26/0000Z 21.7N 76.7W 50 KT 60 MPH

36H 26/1200Z 23.4N 79.4W 55 KT 65 MPH

48H 27/0000Z 24.9N 81.6W 60 KT 70 MPH

72H 28/0000Z 27.1N 84.6W 70 KT 80 MPH

96H 29/0000Z 30.0N 86.5W 80 KT 90 MPH

120H 30/0000Z 32.5N 86.5W 40 KT 45 MPH...INLAND

$$

FORECASTER STEWART

[Macintosh]

The NHC forecast track has this storm spending about 72 hours with the core over open water before impacting the FL panhandle. I've got to believe that's enough time for some real strength surprises to the upside if all goes well. K***ina was a Cat 1 in the Everglades.

[Superstorm93]

Data from the G-IV mission.

Lets see if anything changes with the 00z suite.

[HKY_WX]

Time for some GFS Verifications agains the G-IV data that has been rolling in.

Position: 27N 79W (Near E Florida Coast)

G-IV - 5880 meters

GFS 12z - 5873 meters (7 m too weak)

GFS 18z - 5872 meters (8 m too weak)

Position: 25N 74W (Far NW of Isaac)

G-IV - 5880 meters

GFS 12z - 5873 meters (7 m too weak)

GFS 18z - 5876 meters (4 m too weak)

Position: 21.5N 71.5W (N of Isaac)

G-IV - 5860 meters

GFS 12z - 5856 meters (4 m too weak)

GFS 18z - 5858 meters (2 m too weak)

Position: 21N 74N (NW of Isaac)

G-IV - 5850 meters

GFS 12z - 5851 meters (1 m too strong)

GFS 18z - 5840 meters (1 m too weak)

Generally the soundings indicate the GFS was little bit too weak with the mid-level ridging for both the 12z and 18z runs, with the 18z run being a little bit closer to reality. It will interesting to see how these obs will affect the track of Isaac in subsequent runs.

if thats right, euro ftw.