Tuesday, August 28, 2012

Tropical Storm Isaac: August 27, Update B

Today it looked like the east coast and parts of central Florida were hardest hit from Isaac. They had some massive thunderstorms all day (and yesterday), which are finally diminishing/moving offshore as you can see in the latest infrared satellite image of his convection:

With a center about 300-400 miles away, this shows again just what a big boy he is! He was helping himself to the buffet provided by the deep warm waters of the Florida Current/Gulf Stream off the east coast of Florida, which helped to feed that rainy weather. Comparatively, the west Florida coast got off lightly (so far at least) because we were more-or-less sitting under the deliciously dry air that he was sucking up from the south.

This dry air along with continued wind shear and a lack of deep warm water underneath has really impacted his intensification. There are some areas of strong convection near the center, but they are close to/over those deep warm water patches I previously showed in the sea surface height map. I think he was probably a cat 1 storm earlier today (the circulation has really  been very strong throughout the entire troposphere), but the NHC may just have missed the Love Boat with Isaac (you know I had to get a reference in somewhere! ;-)). Given his disorganized and lopsided appearance now, he’s still classified a Tropical Storm (albeit a very strong TS/border-line cat 1). Officially his winds are 70mph, central pressure 979mb (cat 1 range: 73-95mph). As he gets closer to the northern coast, he will also be impacted a little by the land which will also help inhibit his development. But as he is borderline if the conditions improve just a tad overnight I can see them upgrading him to a weak cat 1 storm.

Apparently I wasn’t completely hallucinating yesterday when I said that I thought he’d move north/NW of the center of the cone track today, towards the right edge of the cone – he just took his time doing it. In the past few hours he has been moving more NNW and now his official center is at 27.1N, 86.8W, heading NW at 10mph (I still think he’s moving a little N of NW). The cone only extends to the middle of MS, but if he continues tracking NNW, he’ll make landfall east of New Orleans.  Even though the MS/AL/FL region is outside the cone, I’d still keep an eye on him until tomorrow afternoon.

<Forecasting/data alert> It is really important that we have data on what is going on off-shore so we can make better estimates of wind speed, direction, and even use it to improve forecasting capabilities. There are a number of coastal ocean observing systems around the US that are being developed to provide us with more detailed information on what is going on out there. I’ll try and show you data from some of them when storms pass by. For today, wind instruments from the COMPS mooring array (run by USF) off the west coast of Florida show measurements of almost 13 m/s, which converts to around 28mph (1m/s =  2.24mph). To look for yourself, go to http://comps.marine.usf.edu/ and you’ll see a map of Florida with some markers. Scroll over one of the markers and the latest wind dial and other data will appear on the left. If you want graphs of the data over the last 24 hours or past few days, click on the mooring, scroll down and click on the graph-looking icon next to the data type you are interested in.  The maximum wind speed I see over the past 24 hours is around 16-17m/s, which is around 35-38mph… so not quite Tropical Storm strength. Unfortunately the station that would have been closest to the storm in this array (farthest out from Florida) is not reporting data at the moment due to a lack of funding.

There are also two NOAA/NDBC moorings in the region – one is slightly northwest of this array and is reporting winds of 27 knots, which converts to 31mph (1 knot = 1.15mph) - not Tropical Storm winds. The other is to the southwest and is reporting winds of 37 knots which converts to 42mph, so definitely weak Tropical Storm winds down there.

There are some FAA observations closer to the northern Gulf coast and Mississippi delta. They are recording winds of around 43 knots, which converts to 50mph. It doesn’t look like any of the surface observations we have support a hurricane at the moment. <end Forecasting/data alert>

Also, speaking of useful data… don’t forget to check tidesonline for storm surge info (I wrote about how to do this yesterday – August 26, Update B). At the moment along the northern Gulf Coast I see a maximum of 1 foot above normal predicted water levels. As the storm passed the west coast, water levels rose from yesterday’s 1-2 feet below normal levels to a maximum of 2 feet above. Here is the water level data from St. Petersburg as an example:

That’s it for today. Everyone stay safe!!

Blogs archived at http://jyotikastorms.blogspot.com/
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DISCLAIMER: These remarks are just what I think/see regarding tropical storms - not the opinion of any organization I represent. If you are making an evacuation decision, please heed your local emergency management and the National Hurricane Center's official forecast and the National Weather Service announcements. This is not an official forecast. If I "run away, run away" (Monty Python), I'll let you know.

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