An evening shift at NHC: A Shary situation

By: Dr. Jeff Masters , 14:57 GMT le 28 octobre 2010

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We have a rare late October triple threat in the Atlantic this morning, three "Invests" with a decent chance of developing. The most serious threat is Invest 91L, a tropical wave centered near 7N 49W, about 950 miles east-southeast of the Lesser Antilles Islands. 91L is moving west to west-northwest at 15 - 20 mph, and will spread heavy rains and gusty winds to the northern coast of South America and the southern Lesser Antilles Islands beginning on Friday night. The system is under low wind shear less than 10 knots, but is too close to the Equator to spin up very rapidly. The storm will also have difficultly developing due to land interaction with South America this weekend. However, several models are indicating the possibility that 91L could develop into a tropical depression in the Central Caribbean by the middle of next week. NHC is giving 90L a 20% chance of developing into a tropical cyclone by Saturday.

A low pressure system (Invest 90L) centered near 27N 42W in the middle Atlantic Ocean has developed a broad and elongated circulation. Heavy thunderstorms on its east side are generating tropical storm-force winds. However, the circulation of 90L has become increasingly stretched out this morning, and the storm is not as well organized as it was last night. NHC is giving 90L a 50% chance of developing into a tropical storm by Saturday.

Finally, a low pressure system (Invest 92L) centered 700 miles south-southeast of Bermuda is developing a surface circulation, and appears very close to tropical depression status. NHC is giving 92L a 60% chance of developing into a tropical cyclone by Saturday. The only land area that might be affected by 92L is Bermuda.


Figure 1. A rare late-October triple threat in the Atlantic: three areas of disturbed weather listed by NHC as areas of interest (Invests) worth running forecast models on. Image credit: National Hurricane Center.

A quiet Tuesday evening shift at NHC
Tuesday evening was a quiet shift at the National Hurricane Center, where I've spent the week as a participant in their visiting scientist program. Each week during hurricane season, NHC invites a hurricane researcher or forecaster in academia, government, or private industry to spend a week shadowing the NHC forecasters as they prepare their forecast products. The evening shift is chosen, since it is less of a zoo, and the presence of the visiting scientist will present less of a distraction to the forecasters.

There was only one area of interest (Invest 90L) on Tuesday. 90L was a disorganized low pressure system in the middle Atlantic that had gotten tangled up with an upper-level low pressure system that was bringing dry air and disruptive wind shear. I worked with senior hurricane specialist Dan Brown, who cheerfully analyzed 90L with me, but confided that this storm was barely worth keeping as an Invest. He lowered its chances of development to 10%, but did order one more run of the various forecast models, so I could see how that was done. He also pointed out two other systems he thought might turn into "Invests" worth watching later in the week, and noted in particular that the large tropical wave approaching South America was unusually vigorous for this time of year, and might be something to be concerned about if it managed to avoid South America and penetrate into the southern Caribbean.

Since there wasn't much else to see on the hurricane end of their operation, I spent the rest of the evening working with NHC's marine forecasting branch. The National Hurricane Center is responsible for preparing weather analysis charts and marine forecasts for the tropical Atlantic and Eastern Pacific, and I worked with meteorologist Felix Garcia of NHC's Tropical Analysis and Forecast Branch (TAFB). He prepared the 8pm Tropical Weather Discussion, and the 00Z tropical analysis chart. I'm highly envious of the software tools NHC has to prepare forecasts and make analysis charts! I want an NAWIPS and ATCF workstation like these guys have, which allows one to zoom, pan, overlay, and quickly change speeds of animations. I'm proud to say that I am responsible for a portion of the 1016 mb isobar on the 00Z tropical Atlantic surface analysis map for Tuesday night, which I drew using the fantastic map drawing software at NHC.

Wednesday evening: A Shary situation
Wednesday evening was a bit more interesting. Invest 90L had been joined by Invest 91L and Invest 92L, and odds for development of 90L had been bumped up to 30%. I spent the first portion of the shift working with TAFB forecaster Wally Barnes, who made the intensity and position estimates of the three invests based on infrared satellite imagery. This task is accomplished using the Dvorak technique, a system of classifying cloud patterns of tropical cyclones based on how cold the cloud tops are, how much spiral banding is present, and other factors. Wally let me determine where the center of 90L was at 00Z last night, and enter the fix into the official database. I am now forever responsible for a tiny piece of the 2010 Atlantic hurricane data base--an awesome responsibility! (It's my first addition to the cause since I sent in my final Hurricane Hunter VORTEX report from the eye of Hurricane Hugo on September 15, 1989, complaining about hitting 5.7 G's of acceleration.) We classified 90L as a T2.0, which is respectable, and meant the system might be on its way to status as Tropical Storm Shary. Wally had to do the analysis for the large, ill-defined tropical wave (Invest 91L), since his eye was much more highly trained to pick out subtle motions in the satellite animations that indicated where the most likely center of circulation might be trying to develop.


Figure 2. "My boat is right here!" Forecaster Wally Barnes of NHC's Tropical Analysis and Forecasting Branch (TAFB) shows where he suspects the center of rotation of Invest 91L might be at 00Z on October 28, 2010.

Wally and I printed out the fix information we'd come up with for 90L, and took it over to Dan Brown, who was working the evening shift again over at the hurricane side of NHC.

"What, you're giving this a T2.0?" Dan good-naturedly hassled us, as we presented the fix info. "You're just trying to get something going for Jeff here so he can see some advisories get issued." Wally defended our analysis, pointing out how the heavy thunderstorms of 90L were pushing closer to the center of circulation, and how the cloud tops had gotten much colder. Dan agreed that 90L really was worthy of more attention, and commented that there was a good chance one of our three invests would probably develop into something NHC would have to issue advisories on before my final shift at NHC ended on Friday night. His prediction was that it would be 92L, the system a few hundred miles north of Puerto Rico.

An hour later, Dan wasn't so sure that 90L wouldn't beat 92L to the title of Tropical Storm Shary. The European ASCAT satellite had just sent in an image of the surface winds over 90L, and ASCAT was showing that the storm had a closed circulation and a respectable area of 40 mph tropical storm-force winds. He gave a call to James Franklin, the head of the hurricane specialist unit at NHC, who was at home. I listened in.

"Hey, I just got ASCAT," said Dan. "It's 35 knots. You can see the center, and the convection is about 130 miles to the northeast. I'm thinking of starting it as a tropical storm, but I hate to start it now, since the convection started at 21Z, and I'd like to see it persist. The ASCAT pass shows the circulation is a bit elongated, and the most recent microwave images are also showing that."

After discussing whether or not to initiate advisories on Tropical Storm Shary for a few more minutes, Dan hung up, then told me the scoop. "This is one of the most difficult parts of the job. It's a real judgment call whether or not to name a storm, when it's such a borderline situation like this. What we're going to do is issue a Special Tropical Weather Outlook mentioning that 90L has gale-force winds, bump the probability of development up to 50 or 60%, watch it for a few more hours, then re-assess." Dan then proceeded to call his replacement, Eric Blake, who was due to work the night shift, to tell him to come in as planned, since it looked like there could well be a Tropical Storm Shary to deal with. Dan then proceeded to write the Special Tropical Weather Outlook and send it out.


Figure 3. "The one that got away was this big!" Wally Barnes tells hurricane specialist Dan Brown what he thinks of 90L's recent burst of heavy thunderstorm activity.

Next update
I'll have an update on Thursday morning from the National Hurricane Center on the latest from the tropics.

Jeff Masters

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Quoting Grothar:


Kudos to you for a good comeback line.



I thank you!
Member Since: 23 juillet 2010 Posts: 1 Comments: 12414
Quoting PSLFLCaneVet:



Dang, we'll have to rule out the caramel apples. It does make my quandary over the selection of candies a bit simpler.


Kudos to you for a good comeback line.
Member Since: Posts: Comments:
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Quoting MrstormX:
Hey guys, who was the member that had the season prediction contest at the start of the season?
Woah where've you been?
Member Since: 14 août 2010 Posts: 10 Comments: 16437
Quoting Grothar:


They don't serve us "kudos" at the home anymore. Hard on the teeth. LOL



Dang, we'll have to rule out the caramel apples. It does make my quandary over the selection of candies a bit simpler.
Member Since: 23 juillet 2010 Posts: 1 Comments: 12414
Quoting MrstormX:


Yah trying to remember what my guess was...


MrstormX,16,6,4,0
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875. JLPR2
Quoting JRRP:


Hmm... I expected to see the circulation a little further to the north.
Member Since: 4 septembre 2007 Posts: 7 Comments: 8506
Quoting jurakantaino:
yes ,Shary will pull Tomas towards her...


Hey, this isn't a romance novel. This is serious business. How you been jurakantaino?
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Quoting Grothar:


Not enough spin at the surface, pressure not falling steadily, winds not sustained. Anything else you want to know?

That about covers it, actually.
Appearances can be sometimes misleading.
But, what a sweet system, right now.
DMax should tell us something or other.
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Quoting Grothar:


OSSGS or something like that. They are still posted.

Yah trying to remember what my guess was...
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871. 7544
91L GETTING mad and says i should have been scary shary but tomas isnt that a greek name too
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You guys are very funny tonight. Keep it up.

Good night all. Early night. I wonder what I'll be waking up to???

Member Since: 17 août 2008 Posts: 0 Comments: 672
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Quoting PSLFLCaneVet:


I stand corrected. Kudos to the voice from the nursing home.


They don't serve us "kudos" at the home anymore. Hard on the teeth. LOL
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867. ryang
Well 91L will start affecting us here in the islands from tomorrow afternoon/evening, so there isn't much time left to prepare.
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Quoting brohavwx:


Well mostly a gut feeling and years of watching these things - I have my own GOES satellite (LRIT) receiving system, but have been getting GOES WEFAX and POES APT since the early 1990's - but I could wrong.

Tell you what, I live in Rockley about 200 yards from Rockley/Accra Beach on the south coast (of Barbados) and will check a couple of old time signs in the morning, if I can, namely;

What we call the white ghost crabs on the beach, just above the high water mark, if they starting marching higher then we in trouble.

If the ants start building higher nest on the lawn, then more rain (as if we need more).

Today, just aftet midday, I saw about a dozen Frigate Birds circling high just inshore of said Rockley Beach high up, one or two at a time, but a dozen or so in tight formation trying to make height, well ... ???

With a system this size, at this time of year, in this area, there is next to no precedent.
I would go with 'the signs' as well, on this one.
Especially the Frigate Birds looking for altitude, preparing to drift away...
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865. JRRP
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Quoting pottery:

Put it into the GOM, and it would overflow the whole thing....


Yeah, according to my rough calculations 91L is about 791.348 miles across right. I am just guessing of course.
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I would not be shocked if we had Tomas sometime tomorrow

91L is really getting its act together
Member Since: 10 Mars 2010 Posts: 1 Comments: 7396
Quoting Grothar:


Not enough spin at the surface, pressure not falling steadily, winds not sustained. Anything else you want to know?


I stand corrected. Kudos to the voice from the nursing home.
Member Since: 23 juillet 2010 Posts: 1 Comments: 12414
Quoting MrstormX:
Hey guys, who was the member that had the season prediction contest at the start of the season?


OSSGS or something like that. They are still posted.
Member Since: Posts: Comments:
Quoting pottery:

Looks better than a TD to me.
What is NHC seeing that we are not?


Agreed. One is forced to wonder. Maybe the good Doc can shed some light for us.
Member Since: 23 juillet 2010 Posts: 1 Comments: 12414
Quoting pottery:

Looks better than a TD to me.
What is NHC seeing that we are not?


Not enough spin at the surface, pressure not falling steadily, winds not sustained. Anything else you want to know?
Member Since: Posts: Comments:
Hey guys, who was the member that had the season prediction contest at the start of the season?
Member Since: Posts: Comments:
Quoting Grothar:
yes ,Shary will pull Tomas towards her...
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Quoting pottery:

Looks better than a TD to me.
What is NHC seeing that we are not?


We need a nice ball of deep convection for it to be classified. Should happen tonight sometime. I expect this to be TD21 tomorrow morning or afternoon.
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Quoting Grothar:


That it is, pot, That it is.


Put it into the GOM, and it would overflow the whole thing....
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Hurricane Lenny

was the 12th tropical storm, eighth hurricane, and fifth category 4 hurricane in the 1999 Atlantic hurricane season. Lenny was the strongest Atlantic hurricane ever recorded in November, and quite unusual in that it moved west-to-east across the Caribbean. Lenny was the first storm to have an extended west-to-east track across the central and eastern Caribbean Sea in the 113-year Atlantic tropical cyclone record.[1]



Highest
winds
1-minute sustained:
155 mph (250 km/h)
Member Since: Posts: Comments:
Quoting Chicklit:


That's what we hear.
Levi suggests it may sit in the caribbean for 10 days or more.

Yes I watched his update shaking my head.
Member Since: 17 août 2008 Posts: 0 Comments: 672
Quoting pottery:

Sorry to hear you say that.
But not surprised.
Looks more serious than stated, right now.


Well mostly a gut feeling and years of watching these things - I have my own GOES satellite (LRIT) receiving system, but have been getting GOES WEFAX and POES APT since the early 1990's - but I could wrong.

Tell you what, I live in Rockley about 200 yards from Rockley/Accra Beach on the south coast (of Barbados) and will check a couple of old time signs in the morning, if I can, namely;

What we call the white ghost crabs on the beach, just above the high water mark, if they starting marching higher then we in trouble.

If the ants start building higher nest on the lawn, then more rain (as if we need more).

Today, just aftet midday, I saw about a dozen Frigate Birds circling high just inshore of said Rockley Beach high up, one or two at a time, but a dozen or so in tight formation trying to make height, well ... ???
Member Since: Posts: Comments:
Quoting reedzone:
One could argue that 91L is ALREADY a Tropical Depression..


Looks better than a TD to me.
What is NHC seeing that we are not?
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847. JLPR2
Quoting pottery:

Agreed.
Even if the center gets as far north as Barbados, we will feel it.
Cant see it getting that far though.


A sudden turn to the north or northeast wouldn't be bad at all. :D
Member Since: 4 septembre 2007 Posts: 7 Comments: 8506
846. JRRP
wao
shary is here
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Quoting pottery:

True.
The dam thing is so big....


That it is, pot, That it is.

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844. JLPR2
It was awesome to see 92L (the relatively most recent invest) beat the other two and get named. XD
Member Since: 4 septembre 2007 Posts: 7 Comments: 8506
843. 7544
looks like 91L will also skip td status and become a ts prrob during dmax tonight dont go to bed yet the best or beast is yet to come lol
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One could argue that 91L is ALREADY a Tropical Depression..

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Quoting JLPR2:


Told you, seems you cant pass on this one. XD

Agreed.
Even if the center gets as far north as Barbados, we will feel it.
Cant see it getting that far though.
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Dr. M has a pretty awesome last name. Would be fitting to see on the bottom of an advisory from the NHC.
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Quoting kimoskee:


Don't need any more rain here in JA.


That's what we hear.
Levi suggests it may sit in the caribbean for 10 days or more.
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Quoting Chicklit:

dare i say monsoonal?


Don't need any more rain here in JA.
Member Since: 17 août 2008 Posts: 0 Comments: 672
837. JLPR2
Quoting pottery:

True.
The dam thing is so big....


Told you, seems you cant pass on this one. XD
Member Since: 4 septembre 2007 Posts: 7 Comments: 8506
Quoting pottery:

True.
The dam thing is so big....

dare i say monsoonal?
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Quoting JLPR2:


There should have been a little note from Masters.
Something like:
MASTERS: WU Community we have Shary, will have an update tomorrow!
XD


LOL

That would be pretty awesome.
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Quoting Orcasystems:


I don't see a compete miss... I think you gonna get wetter

True.
The dam thing is so big....
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Quoting pottery:

Sorry to hear you say that.
But not surprised.
Looks more serious than stated, right now.



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Jeff co-founded the Weather Underground in 1995 while working on his Ph.D. He flew with the NOAA Hurricane Hunters from 1986-1990.

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