Will Hurricane Isaac Make a Comeback?

[Update Update: The probability of ex-Isaac becoming a tropical cyclone is now 50%, and the storm is looking pretty good.]

[Update: The probability of this low pressure system turing into a tropical storm has been increased to 40%. It is moving in the general direction of some relatively warm water.]

Hurricane Isaac was supposed to move, as a tropical storm then as an extratropical low, up the Mississippi, then east across the middle of the US. However, the low pressure system that was once Isaac has instead started to move back south again, and it is now a low pressure system of interest. When I checked last night, there was a very small chance of this low forming a tropical storm, but this morning the probability of this happening is set at 20% (which is a very rough guess). There is a large low pressure system to ex-Isaac's east which is expected to dissipate the energy of the erstwhile hurricane. But, so far, much of what has been "expected" for this storm has not happened exactly as planned. It would be interesting, not unprecedented but a rare event, if ex-Isaac moved back over the Gulf of Mexico, gained strength and got organized into a tropical storm then a hurricane.

Here is a picture of ex-Isaac at the present time, from the NWS Hurricane Center:

The storm that was once Isaac the Hurricane.

In case you were thinking that this has to be some other weather system not related to Isaac, I went to the archives and pulled the GEOS East Satellite images, one per day since mid week, and made them into a moving GIF for you:


More like this

I think the last Gulf hurricane to pull such a move was Ivan in 2004. According to the archives at Weather Underground, it moved off the Delmarva coast as an extratropical low, then drifted southward, crossed Florida, and was reborn as a tropical storm before making landfall as a tropical depression in southwest Louisiana.

I wouldn't wish a hurricane on anybody, but large parts of Texas could use a tropical storm.

By Eric Lund (not verified) on 05 Sep 2012 #permalink

Via een omleiding ben ik op deze site terecht gekomen, en ik vind het uniek dat je zo'n mooi verslag hebt kunnen maken over dit punt. En deze informatie is ook echt leerzaam geweest voor mij omdat ik zelf ervaringen heb gehad over dit onderwerp. Deze website over heeft me ook veel advies gegeven over dit onderwerp.

Weird, because I just heard the rain we had (last night/this morning) in Boston suburb described as "remnants of Isaac."
The rainfall totals from wunderground in the area range from under 2 inches up to 4, mostly around 2.

By Uncle Glenny (not verified) on 05 Sep 2012 #permalink

South Texas please. East Texas has been its usual rainy self since the day last October that PZ , Hitchens, and Dawkins all spoke on the same night in Houston just a few weeks before Hitches died.

Allison did this twice back in 2000. Formed in the Gulf, blew a little and dumped a little rain on Wednesday. Back to sea only to return stronger on Friday night when it dumped 20 inches of rain in three and a half hours. Then due east which put the center of the storm over water again. Then north to flood SW Louisiana. Allison then stayed coherent enough over land to travel over 1000 miles to flood the heck out of Philadelphia.

Uncle Glenny @1731: That's what ex-Isaac was supposed to do: track up into New England and dump a bunch of rain. And part of the storm actually did do that. But some of the storm--certainly most of the vorticity--moved south.

According to the bloggers at Weather Underground, there is some controversy over whether the part that went south was enough of the storm to still be considered Isaac. Jeff Masters says that the NHC does not consider this southern fragment (currently known as 90L) to be enough of Isaac to keep that name, so if 90L becomes a tropical storm it would get a new name. Nadine is the next name on the list.

By Eric Lund (not verified) on 06 Sep 2012 #permalink

What I'm calling ex-isaac is a low pressure system that was definitely part of Isaac, but a huge part of Isaac's energy and moisture tracked east and north as well, and thus the statement about rain in Bostin is also correct. Yeah, even if that had not happened, the storm became sufficiently disorganized to be downgraded to extra-tropical, so it would get a new name even if it didn't send a present to the east coast, I suspect.

The current forecast BTW downgrades the probability of cyclone formation to 40% and the forecasters are sounding less impressed this morning, but the latest satellite views show some blowing up. It will be interesting to see how this tracks through the day.