Friday, October 17, 2014

Hurricane Gonzalo: October 16, Update A

Dear Bermuda, I hope you are ready for whatever tomorrow brings! I hope it brings some clouds, a bit of rain, maybe a strong breeze and short thunderstorm or two, some super high surf, and not much more.

I (and I'm sure you) have been watching Gonzalo the live long day and following, with avid interest, the advisories and forecasts from the NHC so you would have seen that for most of today they had Gonzalo as a cat 4 storm with winds of 145mph. They have now brought him down to 140mph, 943mb - he's still officially a cat 4 storm (cat 4 range: 130-155mph) and the NHC forecast that he'll remain a cat 4 for the next 24 hours (until Saturday night).

I agree that he was looking like a stronger storm today, and he may have been a strong cat 3/weak cat 4 (probably not quite with 145mph winds). He had good outflow in the satellite images, there was a pretty nice and strong eye for most of the day, and wind shear had clearly decreased because clouds weren't streaming off willy nilly. Even the lower level convergence(LLC)/upper level divergence (ULD) that I mentioned a couple of days ago looked better. To show you what the difference is in LLC/ULD between a weak hurricane (my opinion 2 days ago) and a stronger one, I have some figures to show you (from the U. Wisconsin):

Lower level convergence two days ago (when the NHC had him as a cat 3 and I thought he was weaker):
Low lever convergence today (NHC say cat 4, I more-or-less agree):

There are more/tighter concentric rings today, which is what you would expect with a stronger storm.
Upper level divergence two days ago: 
Upper level divergence today: 

As I said, I'm not sure he was as strong as 145mph winds would suggest, but I suspect the reason they kept him at that level was to spur you guys on Bermuda to get ready!

At the last advisory he was at 28.6N, 67.3W, heading NNE at 15mph. The eye looks like it will pass pretty much over/slightly west of Bermuda tomorrow evening:

Having said all that, there are some interesting things in the latest IR satellite loop:
I said yesterday that he would weaken as he got to 30 deg N because the warmer waters underneath the surface of the ocean become shallower around that location. The eye he had all day started to fracture when the 'real' outer bands reached around that latitude, and it looks like the convection is taking a bit of a hit from the lack of deep warm water. The sea surface temperatures are around 28-30deg C, so definitely warm enough to sustain him. The wind shear is still low, but it looks like he'll head into an area of slightly stronger shear tomorrow afternoon.

Here is the image on a larger north Atlantic map:

I wish I could stay awake long enough to see what happens to the center when it reaches around 30 deg N... maybe I'll wake up at 3am to have a quick peek! If that trend continues, Bermuda (located at ~32N) may not get hit by a major hurricane at least. Fingers crossed! (because that's how science works... ;-)).

Regardless, be prepared for something worse and pay attention to your Emergency Managers. And remember: run from the water, hide from the wind!

Stay safe!

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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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