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Thoughts on Isaac, Michael, Kirk, and Leslie

By: Stu Ostro , 1:39 AM GMT on September 05, 2012

If there's one thing that Isaac showed (well, there are several, meteorologically and otherwise, but I think this is the most important one), it was to reinforce how much size matters when it comes to tropical cyclones. It matters, uh, HUGELY for geographical extent of wind and surge impacts, it matters for the height of the surge, and it matters for the duration of the cyclone's effects (and Isaac's slow movement also contributed significantly to that).

Here are satellite images showing the size of Isaac vs. Kirk and Michael. Same scale of the basemap. Yes, some of what shows up on the Isaac image is just cirrus, but the overall appearance of the cyclone vs. the other two is representative of the scope of its circulation and effects relative to the other two.

Images credit: NRL Monterey

Speaking of Michael, this sort of tiny, weak, barely-tropical cyclone being a named storm in the middle of the ocean highlights the changes in observations of such systems now vs. the pre-satellite era. (And for that matter, Kirk being a Category 2 hurricane.) Which in turn fuels debate in trying to assess trends in tropical cyclones related to climate change.

And speaking of Isaac, and of debate, there has been some as to whether the system which triggered flash flooding today in southern Alabama and the western Florida Panhandle, and is en route to the northeastern Gulf of Mexico where models forecast it to regain a more substantial surface circulation, is the remnant of the hurricane. Part of it split off toward the northeast, and its surface circulation became weak and diffuse, but analyses of vorticity (spin) in the lower-middle part of the atmosphere (850 millibars, pictured below, as well as at 700 and 500 mb) show that this feature is most certainly largely the remnant of Isaac.

Image credit: UW-Madison SSEC/CIMSS

And then there's Leslie, which has been struggling, but once it becomes more symmetric its wind field is going to expand and become massive, per the GFS model surface wind field forecast below, and churn up huge waves. (Even if the model doesn't verify perfectly with the location and strength of Leslie at that time, it should be pretty accurate with the overall size.) Already, the storm is large enough to be sending swells to the U.S. East Coast, and its size is going to matter for the nature of effects in Bermuda.

Image credit: Wright-Weather.com

The views of the author are his/her own and do not necessarily represent the position of The Weather Company or its parent, IBM.

Reader Comments

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5. johnmuller
2:27 AM GMT on September 27, 2013
Yes, i think this is right

Soal CPNS dan Kunci Jawaban | Soal CPNS 2013 | Soal CPNS 2014 | CPNS News 2014
Member Since: December 31, 1969 Posts: Comments:
3. ces15hurricanes
10:19 PM GMT on October 15, 2012
Isaac will be the only name retired in the 2012 season. Options: Iker, Isai, Irving, Israel.
Member Since: December 31, 1969 Posts: Comments:
2. WeatherGlob
2:07 AM GMT on September 06, 2012
This illustrates quite well why the NHC need to update their classification system for Hurricanes.

If Kirk was making landfall in the same place that Isaac had made landfall and Kirk was a Cat 2 storm, there would be a lot of press and attention but the effects of the wind and storm surge would have been felt in a much smaller area. People would have said that a Cat 2 storm is not so bad and thought again of evacuating when a Cat 1 storm like Isaac is coming ashore.

It was almost a blessing that Isaac made Cat 1 status. 10 mph less in windspeed and the effects would have been almost identical but the public would have only seen Tropical Storm. Nothing much to worry about. Can't be too bad.

I remember when Ike hit SE Tx in 2008, reading comments from people apologizing for making earlier comments downplaying the fact that Ike was only a Cat 2 storm. Even after all the information put out about how bad the Storm Surge was going to be and the the area that was going to be effected by power outages, most people just heard "Cat 2".

Which is why the NHC need to seriously need to take a hard look at the Hurricane Classification System. Maybe a system the takes an average of the wind speed, storm surge, size of the wind field, and then gives a new "Revised Category Number". Or a system of adding "+" or "++" to the end of the category number if the other ratings of storm surge or size of the wind field are higher than a wind speed reading. Example, Isaac would have been a Cat1++ storm because of the bigger storm surge and larger wind field. Or maybe a "Landfall Category" of the potential damage that will be done by a storm. Isaac was a "LC3" damage category, for example.

The news media and the public like a single number they can latch on to. While the information is out there for all to see, the majority will only look at the simplest number.

We need to start the discussion Now. Billions of dollars are at stake not to mention the lives of those living along the Gulf and Atlantic coasts.

Had to get that off my chest. Thanks for listening.
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1. MrstormX
3:10 AM GMT on September 05, 2012
Isaac trying to pull an Ivan? Only the NHC has the answer.
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Proud to be a weather-obsessed weather geek! \m/ Senior meteorologist at The Weather Channel. If not a meteorologist, would be a DJ ♫

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