Sunday, September 20, 2020

Hurricane Teddy and Tropical Storm Beta: September 20, Update A

Sunday evening... ho hum. 

Hurricane Teddy

He's currently at 29.3N, 63.4W, heading N at 9mph. His outer bands are already passing over Bermuda - just a bit of a breeze and a couple of drops of rain. 

Winds are now 105mph, central pressure is 964mb. This makes him a mid-sized cat 2 hurricane (cat 2 range: 96 - 110mph). We can see he is steadily weakening from his convection:

This infrared satellite image shows mostly green-blues which means that the cloud tops are not as high as before (see the <Science Alert!> and <Technical Alert!> here in case you need a refresher on why that is important), which in turn means that the storm isn't quite as strong as it was even a few hours ago. He still has circulation throughout the troposphere, so I would agree with his hurricane status. His eye is wavering so I would put him at around strong cat 1/weak cat 2 intensity. 

Now, beyond Bermuda the track currently takes him to Nova Scotia and the forecast with winds of 100mph. There is a low pressure front that has been moving eastward from US east coast (actually, it's the same one that TS Beta was caught up in a few days ago - you can see the transition if you look at the vorticity maps from the last few days). The front is almost at Bermuda now, as we see in the vorticity map from the lowest levels of the troposphere (850mph): 

This front (you can see it as that line of higher vorticity stretching to the northeast) is what is going to cause Teddy to move to the northeast a little over the next ~20 hours. They don't think that's enough to keep him on a northeastward track (although I'm not so sure of this). However, higher up in the troposphere is another larger area of low pressure that is currently over Canada, and you can see that in the 500mb (mid-troposphere) map:

He's going to head towards this (once he crosses that first lower troposphere front), and will essentially merge with it - this is when he will actually no longer be a tropical cyclone but a post-tropical storm (or extratropical storm as we used to call them in the good olde days) because he won't be getting his energy from the warm ocean waters (because he'll be over cooler waters). But this system will have a lot of energy from the atmosphere - so he'll still essentially have hurricane-force winds. Not a hurricane per se, but strong enough. The question is how far south from Nova Scotia will he be before he merges and moves off the the northeast. The models are in pretty good agreement that he'll make landfall in Nova Scotia with winds of 105mph. I think he may stay south of Canada (staying on the east side of the Cone of Uncertainty), but some of the winds may still reach the coastline there. I'd get ready for a very blustery sort of day up there, friends! 

Tropical Storm Beta

He's officially at 27.6N, 94.5W, heading WNW at 6mph. He's less than a day from landfall and the NHC expect that to be in Texas, somewhere around Port O'Connor as a Tropical Storm with winds of 50mph, which means he'll be a relatively weak storm. However, the track then has him skirting the coast, as aa Tropical Depression, so it may be breezy sort of week. 

He does have circulation in the lower half of the troposphere, although it's not very circular in structure, but I do think he's closer to being a Tropical Storm today than he has been over the last couple of days. Officially winds are 60mph, central pressure is 995mb, which makes him a mid-sized Tropical Storm (TS range: 39-74mph). The convection has really decreased in the last few hours because of dry air:

I'm not convinced that they have the correct center of circulation - without the convective weather, the satellite imagery seems to show a center that's closer to 28N, 93W - a little more to the east of the official center. However, they sent a plane into the system and that's what they found. I think he's so weak and has such a poor structure that it may just be difficult to find an actual center - I'm not sure he's as strong as they think he is given this poor convection. However, there is a chance that the convection will increase again before landfall tomorrow - we'll see tomorrow. 

That's it for today. Happy Rosh Hashanah!

Ciao for now!


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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