Wednesday, September 15, 2010

Hurricanes Igor and Julia, Tropical Storm Karl: September 15, Update A

Oh dear. I hardly know where to begin today. A rant? Nope, did that earlier already (in person). Sarcasm? Perhaps. Scientific skepticism? Ok then. Glass of wine? Definitely YES, jolly good idea. :-)
I know the NHC have the most up-to-date and bestest information, and they do an amazing job given the stresses and strains of issuing public forecasts of such magnitude, but today I'm afraid I have to disagree with them on the grounds of umm... er... on the grounds of er... well, just because. And so I do a thorough job of this, I disagree with them on all three Atlantic storms out there today. 
Hurricane Igor:
Overnight Igor had 'estimated' winds of 155mph. You might recognize this number. It's the threshold between a Cat 4 and Cat 5 storm. A Cat 5 has winds of 156 mph or higher. The NHC kept him as a Cat 4, but I think for a few hours there he was a cat 5. 1mph in a 155mph storm is well within the error margins and his vorticity was extraordinarily strong. I believe they are reticent to call a storm a cat 5 if they don't have a plane that flies through to provide them in situ  (latin for 'in the place') observations ... which might partly explain why cat 5's rarely form outside the recon flight area. Funny coincidence that, don't you think?
Anyway, he's officially been a cat 4 (range: 131-155 mph) all day today. However he has been weakening for the past few hours and personally I'd say that now he is a strong cat 3 (range: 111-130mph) because the eye is no longer clear, but the NHC are being cautious and keeping him as a weak cat 4 with estimated winds of 135mph and a central pressure of 942mb. He's moving WNW at 8mph, and is currently centered at 19.9N, 55.1W (I think he's moving NW, but that's just me). He's still about 1055 miles southeast of Bermuda, with hurricane force winds found up to 45 miles from the centre, and tropical storm force winds out to 225 miles.
He is moving slightly to the east of the center of cone track, which will take him east of Bermuda. If that trend continues and he carries on weakening, you guys in Bermuda might get away with another kite-flying sort of day. I'm working on that as a plan - I got until about Sunday. ;-)
He's weakening slowly at the moment because that dry air that I've mentioned before managed to creep in (sneaky!). We'll see if it'll keep him in check. Wind shear is not too strong, and water temperatures are still around 29 deg C with 26.5 deg C water in the upper 75-100m. So it's dry air or 'nowt' (a fine northern English colloquial term) that'll keep his intensity down.
Hurricane Julia:
Yeah, so here we start to really disagree. I've been pretty flabbergasted all day today as the NHC persisted in calling Julia a Cat 4 storm. As I suspected yesterday, she was stronger than the NHC had her but I didn't think they'd bump her up to a Cat 4!! Especially as she's the weakest, most pathetic looking cat 4 I've ever seen. I'd go with a cat 3 now, but earlier today I was more inclined towards a strong cat 2. I know she's the farthest east a cat 4 storm has ever been detected, but I am not convinced she ever got to that stage and I don't think I'm the only one who thinks this. But I saved my evidence during the day to make my case in the future if I have to. I completely disagree with the NHC on this one (in case you hadn't figured that out by now ;-)). My evidence includes: 
1. She's over sea surface water temperatures of 27 deg C. Warm enough for a storm, but not particularly high.
2. Sub-surface waters of 26.5 deg C only extend down to in the upper 50-75m.
3. Actual tropical cyclone circulation (vorticity) structure is only in the lowest half of the troposphere. Above that, she's merged with a large front/trough thingy (technical term ;-) ) which is adding to her vorticity, but not in a tropical way.
4. There was an eye, but it's not been clearly defined at all in the visible satellite imagery, which it always is in a cat 4 storm - it's quite cloudy, and at some times it looks like there wasn't really one at all!
5. There is some wind shear - and you can see the impact of that in satellite images as clouds stream off to the northeast from the storm.  
6. They are using estimated winds (135mph) and central pressure (950mb) based on satellite measurements, which are not 100% accurate.
7. This is the farthest east a cat 4 has been detected - surely something like that should have set off alarm bells and warranted further investigation of all these factors?
So, having ranted about this all day to anyone who would listen (i.e. my poor colleagues - I'm sure they have ear plugs by now), I've been trying to work out why they think (and continue to think) she's a cat 4 when ALL signs indicate otherwise. All except their estimated winds - and I'm not privvy to that information but maybe there's a glitch in that system or something? I don't know.    
She's currently at 18.7N, 32.7W (officially they have her at 18.2N, 32.7W, but I think her center is a bit farther north) and is officially moving NW at 15mph. I think she's moving just east of the forcast center of cone track, but still in a general NW-NNW direction. 
Tropical Storm Karl:
He made landfall in the morning (Mexico local time) in the Yucatan, just north of Belize. That warm water I mentioned yesterday did help him to intensify somewhat, and officially he had 65mph winds at landfall, making him a strong Tropical Storm (range: 39-73mph). Guess what... yeah, I disagree. ;-) Sigh. I think he was definitely a weak cat 1 storm at landfall. The convection was really strong, the vorticity signature was strong in the lowest half of the troposphere and had started to pick up in the upper troposphere (a sign he was a hurricane), and there was an eye!! The eye was just visible before landfall on the satellite images, but also on the radar from Belize. However, they kept him as a TS. I think the underestimation of his intensity is because the NHC didn't account for the really deep warm water he was crossing, they only considered the sea surface temperature (at least I didn't see any indication that they were considering the impact the sub-surface water would have). Luckily he was pretty close to land, otherwise he would have grown quite a lot more.
He's still a TS, located at 18.8N, 88.7W and moving W at 14mph. His winds have dropped to 55mph as expected because he's over land. Pressure is 994mb. He's crossing the Yucatan but still has a lot of convection - thunderstorms galore! Fortunately landfall was in a sparsly populated area. The forecast track takes him out into the southern Gulf tomorrow, where he is forecast to intensify to a hurricane before making landfall in Mexico (again). I think he's going to follow the southern edge of the cone, so he won't be over water as much as the track currently suggests. Whether he makes hurricane strength (again in my humble opinion) depends on how long he stays over water. The vorticity in the lowest half of the troposphere remains strong for now.
KF told me that wunderground was showing Karl surviving into the Pacific. I'm not convinced that will happen. He's going to be a remanent low before he gets that far.
That's all I have today. Sorry it's such a long entry...  and I'm so disagreeable! Maybe some ice cream will help. ;-)
We'll see what excitement tomorrow brings! Fun fun!
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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 was there and was going to "run away, run away" (Monty Python), I'll let you know.

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