Tuesday, September 27, 2022

September 27, Update A: Hurricane Ian

It's getting a bit hot out there, so I've got my ice cream and I'm ready to check in on Hurricane Ian...

Track: I, along with a few hundred thousand of my closest friends, have been watching Ian's track shifting to the east (and hence south) all day. He is currently at 24.4N, 83W, heading NNE at 10mph - making that turn towards the east sooner than officially forecast yesterday. This means he will be making landfall tomorrow, not Thursday:

That change in track also means his intensity will be a little different than forecast but more on that later. After landfall, the pressure fields are set up to push him across the state in the general NE direction we see in the official forecast - emerging maybe a little south of where the forecast is at the moment (perhaps the Daytona Beach/New Smyrna Beach area) - but still within that cone of uncertainty so please keep an eye on the entire cone! 

Intensity: He is currently a mid-size cat 3 storm with winds of 120mph, central pressure 947mb (111-129mph). I agree with this estimate. Given that his track has shifted, his intensity will be different as well. There are a couple of things that are working to keep him a little in check. First, he won't be over that deep warm water as much as previously forecast and second, the wind shear has really picked up which you can see in the clouds that are streaming off to the northeast. The eye is already looking worse actually...

And just to show you how far the clouds are streaming off Ian due to wind shear, here's the amazing satellite imagery of half of our planet: 

Yes, you guys in Newfoundland have clouds from Hurricane Ian as well! 

The circulation is still strong throughout the troposphere, but the lower levels are being impacted by that wind shear. If Ian continues to deteriorate, he may be a weak cat 2/strong cat 1 on landfall. Regardless of what he is at landfall, because Florida is a flat and soggy state with Lake Okeechobee in the middle and the Everglades to the south, he will only go down one level by the time he crosses the state - so if he's a cat 2 at landfall, he will be close to a cat 1 on the other side. 

And despite the wind and intensity, at landfall there will still be storm surge...

<Science Alert!> Storm surge is water rising along the coastline as a storm approaches and makes landfall. How high the storm surge is depends on a number of factors: 

1. Storms are low pressure systems, which means that there is low atmospheric pressure. But obviously we don't have a "gap" between the air and the ocean (which are both fluids - one gas and one liquid), so the water 'rises' up to fill that 'gap' which is created by the low atmospheric pressure. So the stronger the storm is, the lower the central pressure, the greater the 'gap' for the water to rise to 'fill'. 

2. Storms are low pressure systems, so in the northern hemisphere they rotate in an anticlockwise direction.  This means generally water will be pushed onshore on the eastern side of the eye (depending on land orientation), and will be pushed off shore on the western side. Storm surge will be higher on the eastern side. Or in this case, on shore south of the eye and off shore north of the eye.

3. Speed of the storm. If a storm is moving quickly, then there is simply less time for water to get pushed onshore before the storm has swung by. Storm surge is greater for slower storms. 

4. Angle of storm approach to land. Depending on if a storm is approaching land directly or at an angle can affect the amount of storm surge because of the direction of the winds. Storms that are heading directly onto shore result in greater storm surge than those that are approaching it from an angle - skirting along the coastline. 

5. Shape of coastline (bays etc). Water can get piled into bays and upstream in estuaries of course. 

6. The depth of the seafloor just off the coast is important. For areas with a shallow seafloor, more water piles up compared to areas where the seafloor is deep just off the coast. 

<End Science Alert!>

To monitor storm surge, I use NOAA's tidesandcurrents website (instructions for this website are in the <Technical Alert!> in this post). At the moment, Key West is already seeing 2 ft above normal levels:

Naples, still to the north of the center, is actually slightly below normal:

And St. Pete levels, even farther north, are dropping as the storm gets closer:

And I know my friends are taking it seriously in Florida when the hurricane supplies move beyond water and wine... 

Be safe out there - listen to your local emergency managers!



Blogs archived at http://jyotikastorms.blogspot.com/

Twitter @JyovianStorm


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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