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Isaac Could Bring 2-4" of Rain to Metro Area

Isaac is already a hurricane based on the latest observations.

Isaac Page

While not officially announced by the NHC, latest hurricane hunter reports show Isaac is now of suffcient strength to be Hurricane Isaac and I believe the 10 a.m. update will reflect that.

Isaac is headed toward the mouth of the Mississippi River and the coast of Louisiana with winds of 75 mph and is moving at 7 mph. Isaac's forward motion has slowed considerably since the 5 a.m. update which doesn't bode well for Louisiana at all. Isaac is currently located about 120 miles from the mouth of the Mississippi River, so at this pace, it won't make landfall for another 12 hours or so. 

DISCUSSION AND 48-HOUR OUTLOOK

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AT 700 AM CDT...1200 UTC...THE CENTER OF TROPICAL STORM ISAAC WAS LOCATED NEAR LATITUDE 27.8 NORTH...LONGITUDE 88.2 WEST. ISAAC IS MOVING TOWARD THE NORTHWEST NEAR 7 MPH...11 KM/H...AND THIS GENERAL MOTION IS EXPECTED TO CONTINUE FOR THE NEXT DAY OR TWO WITH SOME FLUCTUATIONS IN FORWARD SPEED. ON THE FORECAST TRACK...THE CENTER WILL BE NEAR OR OVER THE LOUISANA COAST TONIGHT OR EARLY WEDNESDAY. MAXIMUM SUSTAINED WINDS ARE NEAR 70 MPH...110 KM/H...WITH HIGHER GUSTS. STRENGTHENING IS FORECAST...AND ISAAC IS LIKELY TO BECOME A HURRICANE LATER TODAY. ADDITIONAL STRENGTHENING IS FORECAST UNTIL THE CENTER MOVES INLAND. TROPICAL-STORM-FORCE WINDS EXTEND OUTWARD UP TO 205 MILES...335 KM FROM THE CENTER.

HAZARDS AFFECTING LAND

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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...

* SOUTHEAST LOUISIANA AND MISSISSIPPI...6 TO 12 FT
* ALABAMA...4 TO 8 FT
* SOUTH-CENTRAL LOUISIANA...3 TO 6 FT
* FLORIDA PANHANDLE...3 TO 6 FT
* FLORIDA WEST COAST INCLUDING APALACHEE BAY...1 TO 3 FT

THE DEEPEST WATER WILL OCCUR ALONG THE IMMEDIATE COAST IN AREAS OF ONSHORE WINDS. 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 LARGE AND DANGEROUS WAVES.

WIND...

TROPICAL STORM CONDITIONS ARE EXPECTED TO REACH THE NORTHERN GULF COAST IN THE HURRICANE WARNING AREA THIS MORNING...WITH HURRICANE CONDITIONS EXPECTED BY THIS AFTERNOON. TROPICAL STORM CONDITIONS ARE EXPECTED TO SPREAD NORTHWARD INTO THE FLORIDA BIG BEND AREA AND THE FLORIDA PANHANDLE IN THE TROPICAL STORM WARNING AREA THIS MORNING. TROPICAL STORM CONDITIONS ARE EXPECTED WITHIN THE TROPICAL STORM WARNING AREA IN LOUISIANA BY TONIGHT. TROPICAL STORM CONDITIONS ARE POSSIBLE ON THE COAST OF SOUTHWESTERN LOUISIANA AND THE UPPER TEXAS COAST BY TONIGHT OR EARLY WEDNESDAY.

RAINFALL...

ISAAC IS EXPECTED TO PRODUCE TOTAL RAINFALL AMOUNTS OF 7 TO 14 INCHES...WITH POSSIBLE ISOLATED MAXIMUM AMOUNTS OF 20 INCHES...IN SOUTHEASTERN LOUISIANA...SOUTHERN MISSISSIPPI... SOUTHERN ALABAMA...AND THE EXTREME WESTERN FLORIDA PANHANDLE. THESE RAINS COULD RESULT IN SIGNIFICANT LOWLAND FLOODING. TORNADOES...TORNADOES MAY OCCUR ALONG THE NORTHERN GULF COAST TODAY. SURF...DANGEROUS SURF AND RIP CURRENT CONDITIONS WILL CONTINUE TO AFFECT THE FLORIDA COASTLINE AND PORTIONS OF THE NORTHERN GULF COAST FOR THE NEXT DAY OR SO.

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For us, the main threat is going to be heavy rain. Here's the latest from the Hydrometeorological Prediction Center:

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CONVECTIVE CHANCES SHOULD INCREASE THIS PERIOD FROM NC SOUTHWARD INTO NORTHERN GA..SC AS COLD FRONT SLIPS SLOWLY SOUTHWARD ACROSS THE REGION AND INTERACTS WITH PLUME OF VERY HIGH PWS FEEDING NORTHWARD INTO THE BOUNDARY IN DEEP LAYERED CONFLUENT REGION BETWEEN ISAACS CIRCULATION AND WESTERN PERIPHERY OF WESTERN ATLANTIC RIDGE. WITH PWS EXPECTED TO EXCEED 2.25 INCHES AND MODELS SHOWING INCREASING RIGHT ENTRANCE REGION JET DYNAMICS THAT COULD BE ENHANCED BY OUTFLOW FROM ISAAC...FEEL POTENTIAL FOR SOME SLOW E/W TRAINING BANDS OF HEAVY RAIN WILL BE POSSIBLE..ESPECIALLY FROM NE GA EWD INTO SRN NC..WHERE GENERALLY 1 TO 2 INCH PLUS RAINS WILL BE POSSIBLE WITH ISOLATED HEAVIER AMOUNTS OVER 4 INCHES OR SO GIVEN TROPICAL AIRMASS.

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The NWS here in Atlanta is calling for 2-4" of rain between now and Friday with some isolated areas receiving more. The first band of rain is located between Atlanta and Macon and moving north. 2" has already fallen in some of those areas with more to come. Precipital water values are in the 2.2"-2.3" range (notice how thick the air feels?) so when it does rain, it will be a tropical rain and it comes down hard and fast. Ponding on the roadways will be an issue. Our 3 hour flash Flood Guidance shows that we can get about 3" or so before flooding becomes an issue. 

This post is contributed by a community member. The views expressed in this blog are those of the author and do not necessarily reflect those of Patch Media Corporation. Everyone is welcome to submit a post to Patch. If you'd like to post a blog, go here to get started.

North Georgia Weather September 06, 2012 at 03:02 AM
LOL!!! Yes, I'm still in Cornhusker land and headed back to Atlanta tomorrow! Isn't weather fun! Yes, Isaac made a big circle around a high pressure center and decided to plop back in the Gulf. And guess what? This is what we have now. TROPICAL DEPRESSION THIRTEEN DISCUSSION NUMBER 1 NWS NATIONAL HURRICANE CENTER MIAMI FL AL132012 500 PM EDT MON SEP 03 2012 THE SMALL LOW PRESSURE SYSTEM LOCATED OVER THE CENTRAL ATLANTIC...WHICH DEVELOPED FROM AN UPPER-LEVEL TROUGH...HAS GRADUALLY ACQUIRED ENOUGH ORGANIZED DEEP CONVECTION TO BE CLASSIFIED AS A TROPICAL DEPRESSION. VISIBLE SATELLITE IMAGERY AND AN EARLIER ASCAT PASS INDICATED THAT THE LOW HAS A WELL-DEFINED CENTER AND RELIABLE WINDS OF AROUND 25 KT. THE INITIAL INTENSITY IS SET A LITTLE HIGHER AT 30 KT SINCE ASCAT HAS A KNOWN LOW BIAS AND BECAUSE THE RESOLUTION OF THE INSTRUMENT LIKELY CAN NOT RESOLVE THE SMALL RADIUS OF MAXIMUM WINDS. THE DEPRESSION IS FORECAST TO MOVE SLOWLY WEST-NORTHWESTWARD AROUND THE SOUTHWESTERN PORTION OF A RIDGE OVER THE EASTERN ATLANTIC DURING THE NEXT 24 HOURS. AFTER THAT TIME...THE CYCLONE IS EXPECTED TO TURN NORTHWARD AS THE WESTERN PORTION OF THE RIDGE ERODES.
R++ One of the Famous Dacula Crew September 06, 2012 at 05:59 AM
Well that's political correctness for you, even the "guys" have kids now ...
North Georgia Weather September 06, 2012 at 11:33 AM
:-) Son of Isaac
Jim S September 12, 2012 at 02:07 AM
NGW, this has nothing to do with your post, but I wanted to share that I just took the Storm Spotters class from the NWS, presented be the Gwinnett County EMS. I found this class very interesting and informative, and hope to be able to help with weather spotting!
North Georgia Weather September 12, 2012 at 10:35 AM
That's great Jim! When I took my class, I had to go over to Winder, there was nothing around here in this area. I think Kristi took the class also! I'm also a part of the Spotter Network. http://www.spotternetwork.org/ Their training is a little more rigorous than the NWS class and very thorough. If you liked the NWS training, I think you'll like this too.

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