29 August 2012

As Isaac hits Louisiana, Kirk forms

Isaac was upgraded to a hurricane just before landfall, and actually continued to strengthen as it got closer and closer to the coast.  Not only that, it also stalled, and is sitting in basically the same place for 12 hours and counting.  The full radar loop of Isaac's approach from the New Orleans radar is very illustrative for both the intensification and the stalling.  It first clipped the Mississippi delta on Tuesday evening, then the center moved offshore just a little, and came ashore again about 70 miles west several hours later.  However, hurricanes are large, and damaging effects are always felt very far from the exact center.

 As expected, the storm has caused massive power outages (half a million and increasing) and substantial storm surge.  The surge was almost perfectly forecast by the NHC, and peaked at about 11' in Shell Beach LA, 8' in Bay St. Louis MS, 4' in Mobile Bay AL, 3' in Pensacola FL, and reports of significant surge in Destin FL.  The storm surge will again be a major contributor to the damage, even for a low-end Category 1 hurricane.  Storm surge is intentionally no longer a part of the Saffir-Simpson intensity scale.

The rainfall is another big factor, as was very well forecast by HPC.  Here is the 24-hour rainfall estimate ending at 6am CDT this morning (so obviously the final values will be higher)...

For completeness, I will show the latest satellite image with forecast track overlaid.  Isaac is currently a 70kt Category 1 hurricane, and is drifting to the northwest at 5kts.  The motion is forecast to turn more to the north as it dissipates over land, producing large amounts of rain along its path.


In what seems to be a Circle of Life in the tropics, just as Isaac makes landfall and is destined to dissipate into nothing, Tropical Storm Kirk is born far to the east.  The disturbance that I mentioned in yesterday's first update was upgraded to Tropical Depression 11 at 5pm EDT, and then upgraded again to Tropical Storm Kirk just six hours later.  Kirk is the season's 11th named storm, which is 57 days ahead of climatology, 5 days behind the 2005 mega-season, and 1 day behind the 1995 mega-season.  It's located about 1400 miles southwest of the Azores, truly in the middle of the basin and no threat to land.  It is forecast to strengthen and recurve to the northeast.


And, we have another potent easterly wave to be watching.  This one left the African coast on August 26 and is now about 1600 miles east of the Lesser Antilles.  There is good agreement among global models that this system will develop and be located just northeast of the Lesser Antilles in 5 days, but probably revurve by about 60-65W.  The next name on the list is Leslie.

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