The extremely short-lived Tropical Storm Emily is currently ‘centered’
at 27.5N, 81W, and is now a Tropical Depression with winds of 30mph, central
pressure 1010mb. She is over Florida, heading E at 9mph. She dumped some rain
over southern Florida (although in some parts, I hear it was less than
the daily summer showers) but looks like she’s pretty much done:
I still maintain that she wasn’t a Tropical Storm, and the
vorticity (circulation) signal continues to show that she is part of that front
that extends into the Atlantic. But oh, I don’t think I’ve discussed
vorticity yet this season! How remiss of me. Luckily for you, there isn’t too much more to say about Emily so here’s
a double bill of fun fact-filled <Alerts!> … grab your cup of tea and settle down to tales
of Vorticity and Storm Surge...
Although satellite images are one piece of the information puzzle, the biggest clue about what sort of storm we have is in the vorticity. What that vorticity looks like at different levels of the troposphere gives us a glimpse into the structure of the storm.
All types of stormy weather have a recognizable vorticity
signal in the troposphere. Like a fingerprint, you can figure out what sort of
storm system you have if you know what and where the vorticity is. The
vorticity for low pressure fronts look different compared to tropical storms.
For low pressure fronts, the vorticity stretches out in a long line, which is
what we have for Emily. For proper grown-up Tropical Storms, the vorticity is
confined and generally circular.
You can also tell how strong a tropical storm is depending
on how strong the vorticity is and how high into the troposphere that signal
can be seen. A Tropical Storm ALWAYS has a vorticity signal that reaches the
middle of the troposphere (around 500mb) because this indicates that there is
some deep convection (big thundery clouds). <End Science Alert!>
Luckily, today we have two examples of ‘Tropical Storms’ and
their vorticity (circulation). One of them is actually a Tropical Storm and the
other, well, isn’t. Over in the Pacific, Tropical Storm Irwin is hanging around
with winds of 45mph, which makes him a relatively weak storm (although I think
he may be a bit stronger, based on his strong vorticity field, but that’s
another story).
So, let’s compare the fields in the Atlantic for Emily and
in the Pacific for Irwin at a few different levels of the troposphere:
The lowest level, pretty darn tootin' close to the surface of the planet (850mb)...
Looking a bit higher up (o.k., 700mb if you want to be all
technical ;-))...
Here, Irwin still has a good strong roundish signal, almost but not quite connected to the other blob just to the northwest, and
Emily is still part of a front.
And the middle bit of the troposphere (500mb)...
And again, Irwin’s vorticity signal is round and red (and I think he is stronger than his 45mph would suggest because
he is this well formed at 500mb). But
the signal for Emily is considerably weaker.
Finally, at the highest level (200mb) of the troposphere…
At this height there is no signal for Irwin, which means he is definitely a
Tropical Storm and not a hurricane – we would see a signal this high up if he
was a hurricane. Actually, for a strong hurricane we would see a red splodge
in all levels of the troposphere and they would all line up in each map. The darker red the
splodge is at the 200mb level, the stronger the storm. At this level, of
course there is nothing over Emily either, except a front that is slightly
displaced from the lower levels… all normal stuff really.
These amazing maps are produced by the University of
Wisconsin-Madison's Cooperative Institute for Meteorological Satellite Studies
- and a jolly good job they do too! I will show you how to get them in a future
post, but it’s the same site as the SAL maps: http://tropic.ssec.wisc.edu/tropic.php
that I talked about in early July: http://jyotikastorms.blogspot.com/2017/07/the-atlantic-blob-aka-tropical.html.
The other thing I mentioned in this morning’s post was storm surge…
The top graph shows the water level. In this graph, the red
line is the actual observed sea level, the blue line is what the predicted
water level would be because of the tides, and the green line is the difference
between the two. The height of the green line gives you the storm surge level,
so Trident Pier currently has a storm surge of almost 1ft and slowly rising.
The graph below that is wind speed and direction - you can see the winds
are pretty low. Below that is air pressure which has been fluctuating today,
and below that is air and sea surface temperature (but who cares about that in
a storm, hey? ;-)). <End Technical Alert!>
If Emily does make a funny move tomorrow, I’ll be back. Otherwise I'll try and pop in when the next little blob comes traipsing along.
Oh, and I know I missed Tropical Storm Don but he was another
very short-lived storm so hardly worth the effort really. Too bad as I had a
whole bunch of Godfather jokes lined up but then again, perhaps we’ve had
enough of them in the news lately. ;-)
The next name on the list is Franklin, followed by Gert.
Toodle pips,
J.
--> Blogs archived at http://jyotikastorms.blogspot.com/
Twitter @JyovianStorm
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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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1 comment:
....hope she's a good demure girl and calms down soon🙏🙏🙏
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