An evening shift at NHC: A Shary situation

By: Dr. Jeff Masters , 2:57 PM GMT on October 28, 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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T.C.F.A.
INV/91L/XX
MARK
9.83n/51.72w
Member Since: July 15, 2006 Posts: 178 Comments: 56141
932. JLPR2
Quoting Grothar:


que? LOL


That's puertorican Spanish LOL!

Basically:
Dudes, stop the fooling around, things are bad here... the only thing that we dont need.

Or something like that... XD
Member Since: Posts: Comments:
Quoting Relix:
91L should miss PR.

;-)
slips under PR tracks across east central carb till 71w 17n turns nw n ne e after that this one is a killer
Member Since: July 15, 2006 Posts: 178 Comments: 56141
Quoting KerryInNOLA:
Translate please for us Englishmen. TIA


See 922 - Sorry for being a bilingual man....
Member Since: Posts: Comments:
Quoting sunlinepr:


Aunque los modelos siguen poniendo la trayectoria al sur, lo cual no es bueno, lo unico que nos faltara es que nos coja un Cat. 2 entrando por Guayama y saliendo por Isabela.....


Not all of them. The models have been moving further north and more west.
Member Since: July 17, 2009 Posts: 71 Comments: 27210
Quoting KerryInNOLA:
Translate please for us Englishmen. TIA

He said:

"What I said is that the worst situation for PR is to have a Cat 2 coming through Guayama (SE PR) and going out through Isabela (NW PR)"
Member Since: August 25, 2009 Posts: 20 Comments: 6785
Quoting Jeff9641:


I was 100 percent sure as well until I saw the latest model sweep this afternoon. Track this far south maybe concerning down the road. It maybe hard to believe if you live up north but it is still very hot in FL with heat indexs over a 100 earlier today.


Close to it here. Not a great environment for dissipation.
Member Since: July 23, 2010 Posts: 1 Comments: 12414
Quoting Grothar:


Only from a distance. The inauguration was nice but couldn't see old George too well. All those big wigs everyone wore you know.
Lol.
Member Since: August 14, 2010 Posts: 10 Comments: 17832
OK, I am out ...

Current conditions-
Overcast, cool, still, pressure 1009 falling.
Expecting some rain before dawn.
Dont really know what to expect Friday evening, as yet.
Going to be a busy one tomorrow.
Member Since: October 24, 2005 Posts: 0 Comments: 24913
Member Since: Posts: Comments:
Quoting sunlinepr:


What I said is that the worst situation for PR is to have a Cat 2 coming in through Guayama (SE PR) and going out through Isabela (NW PR)


Thanks. Hopefully that will NOT happen!
Member Since: August 25, 2009 Posts: 20 Comments: 6785
Quoting Bordonaro:

A CAT 2 like Isabelle huh?


What I said is that the worst situation for PR is to have a Cat 2 coming through Guayama (SE PR) and going out through Isabela (NW PR)

Member Since: Posts: Comments:
Quoting Gearsts:
53W and 7.5N thats where i see the broad center's center using the Shortwave (IR2).Anyone here agree?

8.2N & 52.5W
Look at the satellite loop!
Member Since: August 25, 2009 Posts: 20 Comments: 6785
Quoting Jeff9641:
I have a feeling that November will be very active and also have a feeling 91L may have a shot at FL if this ULL digs just off the TX coast instead of close to FL next week. Nogaps solution hints at this possibility.
In november I see a possiblity of 1-3 named storms.
Member Since: August 14, 2010 Posts: 10 Comments: 17832
53W and 7.5N thats where i see the broad center's center using the Shortwave (IR2).Anyone here agree?
Member Since: Posts: Comments:
915. 7544
no one knows where 91l will go almost anywhere is open for now imo
Member Since: Posts: Comments:
Quoting Grothar:


Only from a distance. The inauguration was nice but couldn't see old George too well. All those big wigs everyone wore you know.


That is more what I was looking for earlier. First hand accounts!
Member Since: July 23, 2010 Posts: 1 Comments: 12414
Quoting sunlinepr:


Aunque los modelos siguen poniendo la trayectoria al sur, lo cual no es bueno, lo unico que nos faltara es que nos coja un Cat. 2 entrando por Guayama y saliendo por Isabela.....

A CAT 2 like Isabelle huh?
Member Since: August 25, 2009 Posts: 20 Comments: 6785
Quoting Grothar:


que? LOL


Aunque los modelos siguen poniendo la trayectoria al sur, lo cual no es bueno, lo unico que nos faltara es que nos coja un Cat. 2 entrando por Guayama y saliendo por Isabela.....
Member Since: Posts: Comments:
909. Relix
91L should miss PR.

;-)
Member Since: Posts: Comments:
Quoting 7544:
91L is blowing up at this hour ts by the am ?

Welcome to the 2010 Atlantic hurricane season, anything is possible..91L is looking real good tonight!!
Member Since: August 25, 2009 Posts: 20 Comments: 6785
Quoting sunlinepr:


Mano, dejen el relajo, la cosa que esta mala aqui.... lo unico que nos faltara.....


que? LOL
Member Since: July 17, 2009 Posts: 71 Comments: 27210
Quoting KEEPEROFTHEGATE:
9641 91L IS NOT GOING TO FLA


No need for caps brother.
Member Since: October 8, 2008 Posts: 14 Comments: 4553
Quoting washingtonian115:
Grothar did you see the first president in the flesh?.Haha lol jk.


Only from a distance. The inauguration was nice but couldn't see old George too well. All those big wigs everyone wore you know.
Member Since: July 17, 2009 Posts: 71 Comments: 27210
9641 91L IS NOT GOING TO FLA
Member Since: July 15, 2006 Posts: 178 Comments: 56141
Quoting brohavwx:


I know, and island folk lore should be factored in especially at times like this, but we will see.

I note the ASCAT pass has the surface circulation far to the south and damn near the coast of Suriname, yet satellite animation has much farther north - typical for a forming system, I suppose, but as noted there are no or very few norms for this time of year and position.

Besides the Frigate birds fleeing, what other strange nature things are going on??

Animals/birds have this ESP/6th sense..
Member Since: August 25, 2009 Posts: 20 Comments: 6785
899. 7544
91L is blowing up at this hour ts by the am ?
Member Since: Posts: Comments:
Quoting pottery:

Looks better than a TD to me.
What is NHC seeing that we are not?
they are calling shary because of closeness to bermuda and tomas if convection is to persist with 91 L by 5 am will be tomas mighty tomas
Member Since: July 15, 2006 Posts: 178 Comments: 56141
Quoting JRRP:

me too
eso no me convence no


Mano, dejen el relajo, la cosa que esta mala aqui.... lo unico que nos faltara.....
Member Since: Posts: Comments:
Quoting brohavwx:


I know, and island folk lore should be factored in especially at times like this, but we will see.

I note the ASCAT pass has the surface circulation far to the south and damn near the coast of Suriname, yet satellite animation has much farther north - typical for a forming system, I suppose, but as noted there are no or very few norms for this time of year and position.

Yeah, I was surprised to see the circ. where it is on ASCAT.
You think that could relocate, if convection persists further north?
Member Since: October 24, 2005 Posts: 0 Comments: 24913
Quoting Jeff9641:
91L reminds me of a W-Pac tropical system. Very large circulation.
That is in part to the record sst.Which is why we're seeing these W-PAC type developements.When their in the pre stage they take some time to get going but once they develope.Off they go.
Member Since: August 14, 2010 Posts: 10 Comments: 17832
My pre-season choices were 18, 12, 6, 3.
Doing OK so far, sad to say...
Member Since: October 24, 2005 Posts: 0 Comments: 24913
Quoting pottery:

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...


I know, and island folk lore should be factored in especially at times like this, but we will see.

I note the ASCAT pass has the surface circulation far to the south and damn near the coast of Suriname, yet satellite animation has much farther north - typical for a forming system, I suppose, but as noted there are no or very few norms for this time of year and position.
Member Since: Posts: Comments:
890. JRRP
Quoting JLPR2:


Hmm... I expected to see the circulation a little further to the north.

me too
eso no me convence no
Member Since: Posts: Comments:
Here we can see key conditions that will define 91L's track

Member Since: Posts: Comments:
Quoting Bordonaro:
"Roger, Miami, we have a problem"
91 L will take off over the next few days!!

Compare "Shari" to 91L!!
Member Since: August 25, 2009 Posts: 20 Comments: 6785
Quoting reedzone:


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.
We agree. I'm expecting a TD at 11.
Member Since: Posts: Comments:
Quoting Grothar:


Hey, this isn't a romance novel. This is serious business. How you been jurakantaino?
Grothar did you see the first president in the flesh?.Haha lol jk.
Member Since: August 14, 2010 Posts: 10 Comments: 17832
"Roger, Miami, we have a problem"
91 L will take off over the next few days!!
Member Since: August 25, 2009 Posts: 20 Comments: 6785
Quoting Grothar:


Kudos to you for a good comeback line.



I thank you!
Member Since: July 23, 2010 Posts: 1 Comments: 12414

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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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