New Tropical Depression Forms Off Africa; Forecast to Move NW into Open Atlantic

Tropical Depression Nine Intermediate Advisory Number 1
Nws National Hurricane Center Miami Fl
800 Pm Ast Sun Sep 08 2013

...Rain Bands Approaching The Cape Verde Islands...

Summary Of 800 Pm Ast...0000 Utc...Information
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Location...13.1n 21.4w
About 190 Mi...305 Km Se Of Praia Cape Verde Islands
Maximum Sustained Winds...30 Mph...45 Km/H
Present Movement...W Or 270 Degrees At 12 Mph...19 Km/H
Minimum Central Pressure...1007 Mb...29.74 Inches

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

None

Summary Of Watches And Warnings In Effect...

A Tropical Storm Warning Is In Effect For...
* The Southern Cape Verde Islands Of Maio...Santiago...Fogo...And
Brava

A Tropical Storm Warning Means That Tropical Storm Conditions Are
Expected Somewhere Within The Warning Area...In This Case Within The Next 24 To 36 Hours.

For Storm Information Specific To Your Area...Please Monitor
Products Issued By Your National Meteorological Service.

Discussion And 48-Hour Outlook
------------------------------
At 800 Pm Ast...0000 Utc...The Center Of Tropical Depression Nine
Was Located Near Latitude 13.1 North...Longitude 21.4 West.

The Depression Is Moving Toward The West Near 12 Mph...19 Km/H...And This General Motion Is Expected To Continue Through Late Monday.

A Turn Toward The West-Northwest With A Decrease In Forward Speed Is Forecast By Tuesday.

On The Forecast Track...The Center Of The Depression Should Remain South Of The Cape Verde Islands.

Maximum Sustained Winds Are Near 30 Mph...45 Km/H...With Higher
Gusts.

Strengthening Is Forecast...And The Depression Could Become
A Tropical Storm On Monday.

The Estimated Minimum Central Pressure Is 1007 Mb...29.74 Inches.

Hazards Affecting Land
----------------------
Wind...Tropical Storm Conditions Are Expected To Reach The Southern Cape Verde Islands On Monday.

Rainfall...The Depression Is Expected To Produce Total Rainfall
Accumulations Of 4 To 8 Inches Across The Cape Verde Islands...With
Isolated Maximum Amounts Of 12 Inches Possible...Especially In
Areas Of Mountainous Terrain.

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

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Depression Nine Discussion Number 1
Nws National Hurricane Center Miami Fl
500 Pm Ast Sun Sep 08 2013

Satellite Images Indicate That The Low Pressure System Between The Cape Verde Islands And The West Coast Of Africa Has Developed Enough Convective Organization To Be Designated As A Tropical Depression. The Initial Intensity Is Set At 25 Kt Based On Dvorak Estimates Of T2.0 From Tafb And T1.5 From Sab. The Low-Level Center Appears To Be On The Eastern Edge Of The Deep Convection Due To A Little Bit Of Northeasterly Shear.

The Initial Motion Estimate Is 270/9 Kt. The Depression Is Located
To The South Of A Large Mid-Tropospheric Anticyclone Centered Near
The Azores...And The Current Westward Motion Is Expected To
Continue For Another 36 Hours Or So.

After That Time...The Anticyclone Is Forecast To Weaken While A Closed Mid/Upper-Level Low Develops Near The Canary Islands And A Ridge Builds Westward From Africa.

This Pattern Will Allow The Depression To Turn Rather Sharply To The North-Northwest After 48 Hours And Continue That Trajectory Through The End Of The Forecast Period.

Surprisingly... The Largest Spread Among The Track Guidance Occurs Within The First 48 Hours Or So...But The Models Seems To Converge By 72 Hours. The Nhc Official Track Forecast Is Close To The Model Consensus For Much Of The Forecast.

A Moist Air Mass...Warm Waters...And Relatively Light Shear Should
Allow The Depression To Strengthen At Least Gradually During The
Next Few Days. However...Some Of The Models...Mainly The
Statistical-Dynamical Guidance...Are Fairly Aggressive With The
Intensification Rate After 24 Hours. Ships And Lgem Have Tended To
Have A High Bias This Hurricane Season...So The Official Forecast
Is Kept A Bit Lower.

The Forecast Does...However...Anticipate The Cyclone Becoming A Hurricane By 72 Hours.

Given The Forecast...And The Uncertainty With How Big The Wind Field Will Get Once The Depression Becomes A Tropical Storm...A Tropical Storm Warning Has Been Issued For The Southern Cape Verde Islands.

Forecast Positions And Max Winds

Init 08/2100z 13.1n 20.7w 25 Kt 30 Mph
12h 09/0600z 13.2n 22.1w 30 Kt 35 Mph
24h 09/1800z 13.5n 24.3w 35 Kt 40 Mph
36h 10/0600z 13.9n 26.5w 40 Kt 45 Mph
48h 10/1800z 14.5n 27.9w 55 Kt 65 Mph
72h 11/1800z 17.5n 29.5w 70 Kt 80 Mph
96h 12/1800z 21.0n 31.0w 70 Kt 80 Mph
120h 13/1800z 23.5n 32.5w 65 Kt 75 Mph

Forecaster Berg


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