Proud to be a weather-obsessed weather geek! \m/ Senior meteorologist at The Weather Channel. If not a meteorologist, would be a DJ ♫
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
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