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Issac Approaching Florida Keys Later Sunday: New Forecast Path

By: National Hurricane Center (NHC)
By: National Hurricane Center (NHC)

Tropical Storm Isaac Advisory Number 21
Nws National Hurricane Center Miami Fl
500 Am Edt Sun Aug 26 2012

Summary Of 500 Am Edt...0900 Utc...Information
----------------------------------------------
Location...23.1n 79.0w
About 205 Mi...330 Km Ese Of Key West Florida
About 215 Mi...350 Km E Of Havana Cuba
Maximum Sustained Winds...65 Mph...100 Km/H
Present Movement...Nw Or 305 Degrees At 18 Mph...30 Km/H
Minimum Central Pressure...995 Mb...29.38 Inches

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

A Hurricane Watch Has Been Issued From The Mouth Of The Mississippi River Eastward To Indian Pass Florida...Not Including Metropolitan New Orleans.

The Tropical Storm Warning Has Been Extended Northward And Westward Along The Florida West Coast And The Florida Panhandle To Indian Pass.

The Government Of The Bahamas Has Discontinued The Tropical Storm Warning For The Turks And Caicos Islands.

Summary Of Watches And Warnings In Effect...

A Hurricane Warning Is In Effect For...
* The Florida Keys Including The Dry Tortugas
* The West Coast Of Florida From Bonita Beach Southward To Ocean
Reef
* Florida Bay
* Andros Island In The Bahamas

A Hurricane Watch Is In Effect For...
* The Florida East Coast From Golden Beach Southward To Ocean Reef
* The Mouth Of The Mississippi River To Indian Pass Florida...Not
Including Metropolitan New Orleans

A Tropical Storm Warning Is In Effect For...
* Cuban Provinces Of Ciego De Avila...Sancti Spiritus...Villa
Clara...Camaguey...Las Tunas...Granma...Holguin...Santiago De
Cuba...And Guantanamo
* The Bahamas Excluding Andros Island
* The Florida East Coast From Sebastian Inlet Southward To Ocean
Reef
* Lake Okeechobee
* The Florida West Coast And The Florida Panhandle From North Of
Bonita Beach To Indian Pass...Including Tampa Bay

A Tropical Storm Watch Is In Effect For...
* Cuban Provinces Of Matanzas And Cienfuegos
* The Florida East Coast North Of Sebastian Inlet To Flagler Beach

A Hurricane Warning Means That Hurricane Conditions Are Expected
Somewhere Within The Warning Area...In This Case Within The Next 24 Hours. Preparations To Protect Life And Property Should Be Rushed To Completion.

A Hurricane Watch Means That Hurricane Conditions Are Possible
Within The Watch Area. A Watch Is Typically Issued 48 Hours
Before The Anticipated First Occurrence Of Tropical-Storm-Force
Winds...Conditions That Make Outside Preparations Difficult Or
Dangerous.

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 The Remainder Of Cuba...The Remainder Of Florida...And
The Remainder Of The Northern Gulf Coast Should Monitor The Progress Of Isaac.

For Storm Information Specific To Your Area In The United
States...Including Possible Inland Watches And Warnings...Please
Monitor Products Issued By Your Local National Weather Service
Forecast Office. For Storm Information Specific To Your Area Outside
The United States...Please Monitor Products Issued By Your National
Meteorological Service.

Discussion And 48-Hour Outlook
------------------------------
At 500 Am Edt...0900 Utc...The Center Of Tropical Storm Isaac Was
Located Near Latitude 23.1 North...Longitude 79.0 West.

Isaac Is Moving Toward The Northwest Near 18 Mph...30 Km/H. A West-Northwestward To Northwestward Motion Is Expected During The Next 48 Hours With A Gradual Decrease In Forward Speed.

On The Forecast Track...The Center Of Isaac Is Expected To Move Just North Of The North Coast Of Cuba This Morning...Move Near Or Over The Florida Keys Later Today And Tonight...And Move Into The Eastern Gulf Of Mexico On Monday.

Data From An Air Force Reserve Hurricane Hunter Aircraft Indicate
That Maximum Sustained Winds Have Increased To Near 65 Mph...100 Km/H...With Higher Gusts.

Some Additional Strengthening Is Forecast During The Next 48 Hours...And Isaac Is Expected To Be At Or Near Hurricane Strength When It Reaches The Florida Keys.

Tropical-Storm-Force Winds Extend Outward Up To 205 Miles...335 Km From The Center.

The Latest Minimum Central Pressure Reported By The Aircraft Was 995 Mb...29.38 Inches.

Hazards Affecting Land
----------------------
Rainfall...Total Rainfall Accumulations Of 4 To 8 Inches...With
Maximum Amounts Of 12 Inches...Are Possible Across The Florida
Keys...The Southern Peninsula Of Florida And Portions Of Central And
Eastern Cuba. Total Rain Accumulations Of 3 To 6 Inches Are
Possible Over The Central And Southern Bahamas.

Wind...Tropical Storm Conditions Are Occurring Over Portions Of
Eastern And Central Cuba And The Bahamas And The Turks And Caicos Islands. Hurricane Conditions Are Expected On Andros Island On Sunday. Tropical Storm Conditions Are Possible In Portions Of
Northwestern Cuba By Late Sunday.

Hurricane Conditions Are Expected In The Hurricane Warning Area In
Southwest Florida And The Florida Keys Today...With Tropical
Storm Conditions Expected Later This Morning.

Hurricane Conditions Are Possible In The Hurricane Watch Area In Southeast Florida Today...With Tropical Storm Conditions Expected In The Tropical Storm Warning Area Along The Florida East Coast By This Morning.

Tropical Storm Conditions Are Expected To Spread Northward Along
The West Coast Of Florida And Into The Eastern Florida Panhandle In
The Tropical Storm Warning Area Tonight And Monday.

Hurricane Conditions Are Possible In The Hurricane Watch Area Along The Northern Gulf Coast On Tuesday...With Tropical Storm Conditions Possible By Monday Night.

Storm Surge...The Combination Of A Storm Surge And The Tide Will
Cause Normally Dry Areas Near The Coast To Be Flooded By Rising
Waters. The Water Could Reach The Following Depths Above Ground If The Peak Surge Occurs At The Time Of High Tide...

* Crystal River Through The Big Bend Of Florida...4 To 7 Ft
* Southwest Florida Coast Within Hurricane Warning Area...4 To 6 Ft
* Florida West Coast From Bonita Beach To South Of Crystal River
Including Tampa Bay...3 To 5 Ft
* Southeast Florida Coast And The Florida Keys...1 To 3 Ft
* Central And Eastern Cuba...1 To 3 Ft
* The Bahamas...1 To 3 Ft

The Deepest Water Will Occur Along The Immediate Coast In Areas Of Onshore Flow. Surge-Related Flooding Depends On The Relative Timing Of The Surge And The Tidal Cycle...And Can Vary Greatly Over Short Distances. For Information Specific To Your Area...Please See
Products Issued By Your Local Weather Service Office. Near The
Coast...The Surge Will Be Accompanied By Dangerous Waves.

Tornadoes...Isolated Tornadoes Are Possible Over Portions Of Central And Southern Florida And The Florida Keys On Sunday.

Surf...Dangerous Surf And Rip Current Conditions Will Continue To
Affect The Bahamas...The Turks And Caicos...Eastern And Central
Cuba...The Florida Peninsula And The Florida Keys During The Next
Couple Of Days. Please Consult Products From Your Local Weather
Office For More Information.

Next Advisory
-------------
Next Intermediate Advisory...800 Am Edt.
Next Complete Advisory...1100 Am Edt.

Forecaster Brennan

__________________________________________

Tropical Storm Isaac Discussion Number 21
Nws National Hurricane Center Miami Fl
500 Am Edt Sun Aug 26 2012

While The Satellite Presentation Of Isaac Remains Somewhat
Unimpressive...With Deep Convection Limited To A Rather Small Area
North And East Of The Center...Aircraft Data Suggest That The
Cyclone Has Strengthened A Little Overnight. Peak 850-Mb
Flight-Level Winds Of 69 Kt In The Northeast Quadrant Adjust To An
Intensity Of 55 Kt...Which Is The Value For This Advisory. Aircraft
Data Indicate That The Minimum Pressure Has Also Dropped A Little...To 995 Mb.

Isaac Still Appears To Be Battling The Effects Of Some Low- To Mid-Level Dry Air In The Western Side Of The Circulation...As Seen In Upper-Air Data From Miami And Key West.

Aside From This...However...Conditions Appear Favorable For Steady
Intensification As The Cyclone Move Across The Florida Straits And
Into The Eastern Gulf Of Mexico. Waters Along The Forecast Track Are
Very Warm...And Upper-Level Winds Are Forecast By The Global Models To Become Conducive For Strengthening.

The New Nhc Forecast Is Similar To The Previous One...But Shows A Little Slower Rate Of Strengthening For The First Couple Of Days...Trending Toward The Latest Cycle Of Guidance.

The Initial Motion Estimate Is 305/16...A Little Faster Than Before.

As The Upper-Low To The West Of Isaac Retreats Westward And The
Closed Low Over The Mid-Atlantic States Lifts Northward...Isaac
Will Move Generally West-Northwestward Or Northwestward Around The Western Periphery Of The Atlantic Subtropical Ridge For The Next 48 Hours.

Beyond That Time...There Is Considerable Spread In The Model Guidance. Most Of The Models...With The Exception Of The Ukmet... No Longer Show Isaac Recurving Ahead Of A Shortwave Trough Moving Eastward Across The Eastern United States.

One Camp Of Guidance...Including The Gfs...Hwrf...And Gfs Ensemble Mean Show A Northwestward Track Toward The Central Gulf Coast As The Shortwave Bypasses Isaac Completely. The Ecmwf And Gfdl Show Have More Of A Weakness In The Ridge And Show Isaac Turning Northward Toward The Eastern Gulf Coast.

The New Nhc Forecast Is Faster Than The Previous One Through Much Of The Period...But Is Along The Previous Track Through 36 Hours.

After That Time...A Significant Westward Adjustment Was Made...And The New Nhc Track Is Close To The Tvca Multi-Model Consensus And The Ecmwf...Showing A North-Northwestward And Northward Turn At Days 3 Through 5.

Given The Large Spread In The Guidance...Confidence In The Long-Range Track Forecast Is Quite Low...And It Is Too Early To Determine Exactly Where And When Isaac Will Make Landfall Along The Gulf Coast. Further Adjustments To The Track May Be Necessary Later Today.

Throughout The Period...It Is Important Not To Focus On The Exact
Forecast Track Since Significant Hazards Extend Well Away From The
Center.

Given The New Nhc Forecast...A Hurricane Watch Has Been Issued For A Portion Of The Northern Gulf Coast.

Forecast Positions And Max Winds

Init 26/0900z 23.1n 79.0w 55 Kt 65 Mph
12h 26/1800z 24.2n 80.8w 60 Kt 70 Mph
24h 27/0600z 25.5n 83.1w 65 Kt 75 Mph
36h 27/1800z 26.9n 84.9w 70 Kt 80 Mph
48h 28/0600z 28.1n 86.5w 80 Kt 90 Mph
72h 29/0600z 30.2n 88.0w 90 Kt 105 Mph
96h 30/0600z 32.0n 88.5w 40 Kt 45 Mph...Inland
120h 31/0600z 34.0n 88.5w 25 Kt 30 Mph...Inland

Forecaster Brennan


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