Tuesday, July 06, 2021

Tropical Storm Elsa: 6 July, Update A

Another busy bees sort of day today (I say with ice cream beside me for er... brain food).

Our Tropical Storm du jour has crossed the Florida Keys and is now at 25.8N, 83W, heading N at a slower 10mph in the Gulf of Mexico:

Elsa emerged from Cuba and was a little stronger than the official forecast expected and is now a very strong Tropical Storm/almost cat 1 hurricane with estimated winds of 70mph, central pressure is 1000mb (TS range: 39-73mph).  She will most likely continue in this approximate strength of strong TS/cat 1 storm on landfall as expected yesterday and nothing too much stronger than that because the conditions aren't in place for intensification beyond that. You can see that she is under some wind shear in the satellite imagery because most of the convection is to the eastern side of her circulation:

Although she's lopsided, unfortunately for Floridians, the tougher weather is on your side - lots of rain, thundery weather, and possible tornadoes.

Storm surge is also increasing along the coast. To look for yourself...

<Technical Alert!> How to look up Storm Surge: Go to NOAA's website: tidesandcurrents (https://tidesandcurrents.noaa.gov/). If you click on this link, you will see an ugly cartoonish bad-suntan coloured map of the US (in shades of orange to represent the land - which, with the heat wave last week may just be the colour of land anyway these days!). Click on the state that you are interested in e.g. Florida. This will show you a much nicer colour map with a bunch of pins. These are the locations of the stations. You have to be careful though (if you are on a Mac especially) because the map is not static so you can accidentally scroll around and end up in the middle of the Atlantic, and will have to zoom out until the map you want re-appears and then zoom back in. Surely there must be a better map to use? 

You can either locate the nearest station by entering the area you are interested in, or zoom into the map. Click on that station, and in the lower left is a button that says 'plot'. Click that on and it will show you a plot of the expected water level (in red) and the actual measured water level (in blue). Here is the plot from Ft. Myers:

By scrolling your mouse over the plot, the numbers appear showing the actual values (and then you have to do some complicated maths to get to the difference between the two). In this case, you can see that the highest storm surge was actually about 0.63ft above normal a few hours ago and it is now returning to the predicted water levels. As Ft. Myers is up an estuary, I expect this is the storm pushing water into the estuary on the side where this sensor is located. 

If you want to see the corresponding winds, air pressure and other handy-dandy data, you can scroll down. So here, for example, is the pressure field which clearly shows the point at which the storm was closest to this location - which corresponds to the time in the water level plot above, when the storm surge (red) started to decrease towards the predicted level (blue) - because the winds were no longer pushing the water up against that side of the estuary. 

Having a quick look at other locations, water levels in St. Petersburg (my old home) is currently just over 0.5ft above normal and increasing (which is the case across most of Tampa Bay), and the pressure there is still decreasing as the storm gets closer, but Cedar Key to the north, which always has a higher storm surge is already at 1ft above normal - I assume their sensor is in a location which means water gets pushed up against it. <End Technical Alert!> 

And if you want to have a look at data offshore, check out the University of South Florida College of Marine Science COMPS network (these are the moorings I got my PhD data from a <ahem> couple <ahem> of years ago ;-)), which is part of the Southeast Coastal Ocean Observing System and the Gulf of Mexico Coastal Ocean Observing System:

The air pressure at the mooring closest to the Tropical Storm (C13) is currently reading 1002mb which is close to the levels the NHC are reporting, but winds are only just over 30mph though, so not quite the same intensity as being reported... I do see stronger winds at other moorings but I'm not sure this storm is quite as strong as they are estimating. This is a good example of why we need good observations off shore as well as a better understanding and data for storms in general! 

Listen to your local emergency managers because they have the best local information. Even with a strong Tropical Storm, remember, run from water, hide from the wind - which means that if you are in an area that floods, move to higher ground, otherwise hunker down. Most fatalities in storms are caused by water-related issues!

And I hope you are all prepared... here's a checklist from 2016, just in case (thanks Mark Z.):

Be safe my peeps!




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 local 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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