Tuesday, November 19, 2013

Subtropical Storm Melissa: November 18, Update A

Really? Subtropical Storm Melissa? Really?? Sigh. Sorry to break it to you all, but this is not a subtropical storm. Luckily it's late now, the season is almost over, and I've had a lovely glass of wine otherwise I'm sure I'd be ranting about this! ;-) 

She is supposedly at 30.3N, 54.7W, heading NW at 8mph. Winds are 60mph, central pressure 985mb. This is what she looks like in the infrared satellite image: 

So, why is Melissa not a subtropical storm? (Apart from the obvious lack of deep convection, which we know by the dearth of orange and red colours in the image above... it's just a light drizzle at the most!).

The biggest clue is in the circulation (or vorticity as this is supposed to be all sciency ;-)) and what that looks like at different levels of the troposphere - this gives us a glimpse into the structure of the storm. I'm sure you all remember that a tropical storm has a very well defined circular pattern of vorticity... (and just in case you happened to have forgotten that, there's an extremely funny and well-written refresher here: 
http://jyotikastorms.blogspot.com/2013/09/tropical-storm-gabrielle-hurricane.html). Well a subtropical storm would have that lovely circular pattern in the lower levels, and would be connected to a larger area of stronger vorticity (like a front) in the upper levels. Melissa looks like she's connected to a stream of stronger circulation and is not well defined at any level of the troposphere. Here are the latest circulation/vorticity maps for four levels of the troposphere. 

The lowest level, pretty darn tootin' close to the surface of the planet: 

A bit higher: 

The middle bit:

And the upper troposphere: 

None of these show that well defined circulation we'd expect to see with a subtropical or tropical storm! So this is more of an extratropical storm methinks.

She's heading NW for now, but is expected to turn north, then NE, and then turn left at the MacDonalds on Thursday:

I haven't had time to look at the track possibilities, but I'm advising all fish in the area to board up your fish holes and take a holiday... the South Atlantic is looking particularly nice at this time of year. ;-)

I have a travel/meetings day tomorrow, but I'll try and pop back on from some airport or another.  In the meantime I'll leave you with a very cheery thought... only 5 more days until the new Dr. Who 50th Anniversary Episode!!! :-) :-) 

Night night!


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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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