Tropical Storm Isaac Advisory Number 12
Nws National Hurricane Center Miami Fl
1100 Pm Ast Thu Aug 23 2012

Summary Of 1100 Pm Ast...0300 Utc...Information
-----------------------------------------------
Location...16.7n 68.7w
About 145 Mi...235 Km Sse Of Santo Domingo Dominican Republic
Maximum Sustained Winds...45 Mph...75 Km/H
Present Movement...Wnw Or 290 Degrees At 18 Mph...30 Km/H
Minimum Central Pressure...1001 Mb...29.56 Inches

Watches And Warnings
--------------------
Changes With This Advisory...

The Hurricane Warning For Haiti Has Been Changed To A Tropical Storm Warning And A Hurricane Watch.

The Government Of Cuba Has Issued A Tropical Storm Warning For The Cuban Provinces Of Camaguey...Las Tunas...Granma...Holguin...
Santiago De Cuba...And Guantanamo.

The Government Of Cuba Has Issued A Tropical Storm Watch For The
Cuban Provinces Of Ciego De Avila...Sancti Spiritus...And Villa Clara.

The Tropical Storm Warnings For Puerto Rico...Vieques...Culebra...
And The U.S. Virgin Islands Have Been Discontinued.

The Government Of Antigua And Barbuda Has Discontinued The Tropical Storm Warning For The British Virgin Islands.

The Government Of The Bahamas Has Issued A Tropical Storm Watch For Andros Island And The Central Bahamas Including Cat Island...The Exumas...Long Island...Rum Cay...And San Salvador.

Summary Of Watches And Warnings In Effect...

A Hurricane Watch Is In Effect For...
* Haiti

A Tropical Storm Warning Is In Effect For...
* Dominican Republic
* Haiti
* Cuban Provinces Of Camaguey...Las Tunas...Granma...Holguin...
Santiago De Cuba...And Guantanamo
* Southeastern Bahamas Including The Acklins...Crooked Island...Long Cay...The Inaguas...Mayaguana...And The Ragged Islands
* Turks And Caicos Islands

A Tropical Storm Watch Is In Effect For...
* Cuban Provinces Of Ciego De Avila...Sancti Spiritus...And Villa
Clara
* Andros Island And The Central Bahamas Including Cat Island...The
Exumas...Long Island...Rum Cay...And San Salvador

A Hurricane Watch Means That Hurricane Conditions Are Possible
Within The Watch Area...In This Case Within The Next 24 To 36 Hours.

A Tropical Storm Warning Means That Tropical Storm Conditions Are
Expected Somewhere Within The Warning Area Within 36 Hours.

A Tropical Storm Watch Means That Tropical Storm Conditions Are
Possible Within The Watch Area...Generally Within 48 Hours.

Interests In Jamaica...The Remainder Of Cuba...The Remainder Of The Bahamas...South Florida...And The Florida Keys Should Monitor The Progress Of Isaac.

Discussion And 48-Hour Outlook
------------------------------
At 1100 Pm Ast...0300 Utc...The Center Of Tropical Storm Isaac Was
Located Near Latitude 16.7 North...Longitude 68.7 West.

Isaac Is Moving Toward The West-Northwest Near 18 Mph...30 Km/H...And A West-Northwest To Northwest Motion At A Slightly Slower Forward Speed Is Expected Over The Next Couple Of Days.

On The Forecast Track...The Center Of Isaac Will Be Near Or Over Hispaniola On Friday...And Move Near Or Over Southeastern Cuba On Saturday.

Maximum Sustained Winds Are Near 45 Mph...75 Km/H...With Higher
Gusts. Some Strengthening Is Forecast While The Center Remains Over Water.

Tropical Storm Force Winds Extend Outward Up To 185 Miles...295 Km From The Center.

Estimated Minimum Central Pressure Is 1001 Mb...29.56 Inches.

Hazards Affecting Land
----------------------
Wind...Tropical Storm Conditions Are Expected Over Portions Of The
Dominican Republic And Haiti On Friday...With Hurricane Conditions
Possible Over Portions Of Haiti. Tropical Storm Conditions Are
Expected Over The Southeastern Bahamas And The Turks And Caicos Islands By Late Friday. Tropical Storm Conditions Are Expected Over Eastern Cuba By Late Friday Or Early Saturday. Tropical Storm Conditions Are Possible Over Central Cuba...The Central Bahamas...And Andros Island By Saturday.

Rainfall...Total Rainfall Accumulations Of 8 To 12 Inches...With
Maximum Amounts Of 20 Inches...Are Possible Over Hispaniola.

These Rains Could Cause Life-Threatening Flash Floods And Mud Slides.

Total Rain Accumulations Of 2 To 4 Inches...With Maximum Amounts Of 6 Inches Over Higher Terrain...Are Possible Over Puerto Rico And The Virgin Islands. Total Rain Accumulations Of 2 To 4 Inches Are Possible Over The Southeastern Bahamas.

Storm Surge...A Storm Surge Will Raise Water Levels By As Much As 2 To 4 Feet Above Normal Tide Levels In Areas Of Onshore Winds Along The Coast Of Hispaniola.

Near The Coast...The Surge Will Be Accompanied By Dangerous Waves.

A Storm Surge Will Raise Water Levels By As Much As 1 To 3 Feet Above Normal Tide Levels In Areas Of Onshore Winds Along The Coast Within The Remaining Tropical Storm Warning Area.

Surf...Dangerous Surf And Rip Current Conditions Will Affect The
Leeward Islands...Virgin Islands...Puerto Rico...Hispaniola...The
Southeastern Bahamas...And The Turks And Caicos During The Next
Couple Of Days.

Next Advisory
-------------
Next Intermediate Advisory...200 Am Ast.
Next Complete Advisory...500 Am Ast.

Forecaster Pasch
____________________________________________________

Tropical Storm Isaac Discussion Number 12
Nws National Hurricane Center Miami Fl
1100 Pm Ast Thu Aug 23 2012

Observations From A Noaa Hurricane Hunter Aircraft Suggest That
Isaac Has Strengthened Only Slightly This Evening.

Flight-Level And Sfmr-Observed Surface Winds From The Aircraft Suggest That The Current Intensity Is Near 40 Kt. The Storm Continues To Have Fairly Strong Upper-Level Outflow And...If The Inner Core Becomes Better Defined...Has An Opportunity To Strengthen As Long As It Remains Over Water.

However...The Center Of The Storm Is Forecast To Move Over Southwestern Hispaniola In 12 Hours Or So...And This Would Halt Any Intensification.

A Little Later On...Land Interactions With Eastern Cuba Would Also Inhibit Intensification Or Cause Weakening.

Isaac Will Likely Restrengthen When It Moves Over The Straits Of Florida And The Eastern Gulf Of Mexico In The Latter Part Of The Forecast Period.

However It Should Be Noted That There Is Significant Uncertainty In Tropical Cyclone Intensity Predictions At 3-5 Days.

The Initial Motion Estimate Is 290/16.

A Mid-Tropospheric Trough Over The Southeastern U.S. Is Causing A Break In The Subtropical Ridge.

In Response To This...Isaac Should Turn Toward A More Northwestward Heading Over The Next Few Days.

The Model Consensus Has Shifted A Bit To The Right During The First Half Of The Forecast Period...Primarily Due To An Eastward Shift Of The Latest Gfs Track. The Official Forecast Is Nudged A Bit To The Right Of The Previous One And Is Somewhat Faster Based On The Latest Model Guidance.

The Initial And Forecast Wind Radii Have Been Expanded Based On Buoy And Ship Data. It Is Important Not To Focus On The Exact Track
Because Of Forecast Uncertainties And The Fact That Isaac Has A
Large Area Of Tropical Storm Force Winds Associated With It.

A Synoptic Surveillance Mission By The Noaa G-Iv Jet Aircraft Has
Been Conducted To Collect Atmospheric Observations In The
Large-Scale Environment Of Isaac. These Data Will Be Assimilated
Into The 0000 Utc Runs Of The Global Models...And Should Improve
The Accuracy Of Their Forecasts For The Next Advisory Cycle.

Forecast Positions And Max Winds

Init 24/0300z 16.7n 68.7w 40 Kt 45 Mph
12h 24/1200z 17.5n 70.7w 55 Kt 65 Mph
24h 25/0000z 18.8n 73.1w 45 Kt 50 Mph
36h 25/1200z 20.2n 75.4w 45 Kt 50 Mph...Inland
48h 26/0000z 21.8n 77.7w 45 Kt 50 Mph...Inland
72h 27/0000z 24.8n 82.0w 55 Kt 65 Mph...Over Water
96h 28/0000z 27.5n 85.5w 70 Kt 80 Mph
120h 29/0000z 30.0n 88.0w 80 Kt 90 Mph

Forecaster Pasch
____________________________________________________

Oscar's remarks...

Isaac is presenting an interesting case study...and it appears TWO main possibilities for Isaac's path are emerging - BOTH of which would be favorable for the WTVY-TV coverage area.

The possibility of Isaac churning through the eastern Gulf of Mexico toward the nearby Florida panhandle cannot be ruled out, but for now, it seems the least likely scenario.

Here's why:

1) -
The trough on top of our area over the last 2 weeks is amplifying (narrowing) and being pushed southeast. Why?

A low pressure system in the Pacific northwest is pushing eastward.

As this NW U.S. low moves east, a high pressure ridge builds and moves east across the central U.S.

This, in turn, is responsible for amplifying and pushing the southeastern U.S. trough to the southeast.

The KEY to this scenario is how fast this NW U.S. low moves east.

If the low pushes faster, the central U.S. ridge builds faster and then pushes the southeastern trough faster southeast. This trough would then be in a better position to pick up an approaching Isaac. If so, then Isaac could still be whisked across the Florida PENINSULA over to the Atlantic side and head up the east coast of the U.S.

If this whole process is slower, then the southeastern trough may not dig as far southeast...instead the trough would lift out quicker and miss picking up Isaac.

We should know if this scenario is correct by early this weekend.

2) -
So, if the trough does not pick up Isaac - what next?

As the southeastern trough lifts out, high pressure fills the void left behind. Originally, it appeared the high pressure would quickly build in from the east, but only stretch as far west as central Georgia. This left a 'weakness' in the atmosphere - simply put, an area of lower pressure that the high pressure would steer Isaac toward.

That area unfortunately is our area. The computer guidance model signaling this trend earlier this week was considered not likely.

However, other guidance trended toward that thinking, believing the southeastern trough would not be around to pick up Isaac - thus Isaac would indeed cross into the Gulf.

In the meantime, the computer model (by the way, it's called the European, or ECMWF) that first signaled this west trend, has, in subsequent model runs, depicted the southeastern ridge building farther west from Georgia.

Now (late Thursday evening), this weather model aims Isaac toward the Louisiana / Texas border the middle of next week.

At the same time owing to the past accuracy of the ECMWF model, the National Hurricane Center has shifted Isaac's landfalling path farther west to near Mobile.

I believe the NHC's western shift will continue on Friday, closer to Louisiana at least as a compromise landfalling path.

This particular weather model (ECMWF) has been excellent this season in its tropical predictions. Of course, with changing weather conditions the ECMWF model's guidance may change as well. For now, there's no sign of that.

Concluding, there is still a possibility of the southeastern trough deflecting Isaac across Florida into the Atlantic and up the eastern U.S. coast.

The (so far so good) ECMWF weather model says that will not happen - INSTEAD, Isaac goes into the Gulf and heads for the vicinity of the Louisiana / Texas border by the middle of next week.

In the meantime, don't be caught napping..go over what you would and should do if Isaac does come this way. If it does, then you are ready. If not, you succeeded in preparing yourself, family, pets and livestock for the worst.