Wednesday, September 12, 2018

Hurricanes Florence and Helene, Tropical Storms Isaac and Olivia: September 12, Update A

Welcome to mid-September - on average, statistically the busiest part of the Hurricane Season:
(Credit: NOAA)
In reverse order... 

Tropical Storm Olivia: She's at 20.9N, 154.2W, heading W at 15mph. She's a relatively weak TS now with winds of 50mph, central pressure of 1005mb. She'll hit Hawaii today, but will really be a little breezy with a few drops of rain here and there. This is my last post on Olivia.

Tropical Storm Isaac: He's a little weaker than yesterday with winds of 65mph, central pressure 999mb. He's currently at 14.5N, 53.0W, heading W at 16mph and should be crossing the Lesser Antilles in the Caribbean on Thursday. The dry air took it's toll and he still isn't through it all:

He still has some convection, as we can see from the infrared satellite imagery: 
He has almost no circulation (vorticity) in the upper troposphere, but it's pretty good in the lower half, so he's definitely a Tropical Storm. He is moving over warmer water now, which will keep that convection going, but I agree with the forecast that he'll remain a TS as he gets to the islands: 

Hurricane Helene: She's still a cat 2 storm with winds of 100mph (cat 2 range: 96-110mph), central pressure of 973mb. She's at 18N, 35.4W and has taken a northward turn and is heading NW at 10mph:
She still has a very strong circulation (vorticity) in the upper troposphere, which is a sure sign she's a hurricane:
She's also been battling dry Saharan Air, and is not over as warm water as Isaac, and she's under some wind shear so her convection is a bit wishy-washy (technical term ;-)): 
But despite that, you can still see her eye which is an indication of just how strong and robust she was. A weaker storm would have crumbled by now. 

Hurricane Florence: And that brings us to our little Florence, the storm that's had one-to-many turns on the Magic Roundabout! She's currently a mid-size cat 4 with winds of 140mph (cat 4 range: 131-156mph), central pressure 946mb:
The eye is strong with this one, and we know she has good vorticity throughout the troposphere, so her structure is good, as is the convection surrounding the eye (that red indicates high cloud tops, which means strong thundery activity): 
The marginally good news is that she is experiencing some wind shear, which is why that convection is a little lopsided - it looks like that will carry on for at least a day, so she should be weakening a tad in that time (to perhaps a cat 3). 

She's currently at 28.5N, 69.5W, heading WNW at 17mph:
Although the track is showing landfall near the Wilmington, NC area at the moment, there is a lot of strong convection to the north as well, so pretty much everyone in that area should expect many buckets of rain. If you are umming and ahhing over whether or not to evacuate, a good rule of thumb is to run from the water, hide from the wind. If you decide to evacuate, don't forget your children, pets, and of course, the wine...

Reminders: listen to your local emergency managers. And if she is a major storm at landfall in your area, you may not be able to get back to your home for a few days (or weeks). 

Finally, over on the other side of the world, Super Typhoon Mangkhut, currently a cat 5 storm, with winds of 157mph (cat 5 range: higher than 156mph) is heading to the Philippines... landfall in about three days.  
More tomorrow!

Twitter: jyovianstorm
These remarks are just what I think/see regarding tropical storms. If you are making an evacuation decision, please heed your local emergency management and the National Hurricane Center's official forecast. This is not an official forecast.

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