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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Quoting Chicklit:


..maybe they just have the satellite positioned in the wrong place, oops.
Doc is probably fiddling with the knobs again...when I saw that loop of andrea I though wow I am looking in the wrong place!! then I saw the date..
Member Since: September 1, 2009 Posts: 23 Comments: 1007
Quoting reedzone:
Shear is 10 knots over 92L, expect further strengthening into Subtropical Storm Shary later tonight into tomorrow morning. Shear is low going towards Bermuda as well. I would not be surprised if this makes it to 60 mph. when it gets going.


I doubt it will reach 60 mph...50 mph at most in my opinion. Shear will be on the increase after tomorrow, and its not really in the most favorable environment, up to 20 knots of shear.
Member Since: July 6, 2010 Posts: 113 Comments: 32833
Quoting JRRP:


hey hey ...


I see more jumped on board. :-/
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great pic reed
Member Since: July 11, 2006 Posts: 14 Comments: 11423
Quoting TOMSEFLA:
stormw mush of got the boot over at hurricane hollow also


why would you say that? He was on the show just last week
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Is it really late October?? Seems like late September.

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627. JRRP


hey hey ...
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Quoting pottery:

Maybe cancelled.
60 people to move by boat to Monos Island, to party on Saturday.
The Gulf of Paria is pretty benign, most times.
But SouthWesterlies and Westerlies turn it into a Bad place to be, in a small boat.
The jetties and piers on the islands off the NW peninsula are not built to be landed on in rough conditions, and ALL the marinas are west-facing...

We have that problem here.. because of the trades most anchorages,docks etc are open to the SW.. so when storms go by and the winds come from there we lose boats and when you add in the north swell from storms there is almost no where to put your boat..
Member Since: September 1, 2009 Posts: 23 Comments: 1007
91L looks like the mothership, sheesh.

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Quoting washingtonian115:
Obviouisly some off you all don't seem to remember Andrea from 2007.She formed in a dry,and stable envierment with shear.Which is why she was a SUB-tropical system.Her core also had cold air in it like this one dose.


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Quoting HurricaneDean07:
its a good thing too. the NHC people would be tearing their hair out without him to help. Theres going to be a pretty big blog on what happend tonight at the NHC


I think the NHC can handle the pressure without him... :P
Member Since: October 15, 2008 Posts: 11 Comments: 2312
.
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Quoting sailingallover:

We cannot be looking at the same thing..You are talking about this lopsided dry air intruded upon convectionless wimp?



..maybe they just have the satellite positioned in the wrong place, oops.
Member Since: July 11, 2006 Posts: 14 Comments: 11423
Shear is 10 knots over 92L, expect further strengthening into Subtropical Storm Shary later tonight into tomorrow morning. Shear is low going towards Bermuda as well. I would not be surprised if this makes it to 60 mph. when it gets going.
Member Since: Posts: Comments:
Obviouisly some off you all don't seem to remember Andrea from 2007.She formed in a dry,and stable envierment with shear.Which is why she was a SUB-tropical system.Her core also had cold air in it like this one dose.
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Quoting Hurricanes101:


Sub-Tropical, hence the appearance

I bow to the more enlightened.
I am not familiar with ST systems.
It just looks a bit anaemic, to me.
Member Since: October 24, 2005 Posts: 0 Comments: 24883
Quoting KerryInNOLA:
Can't see any of these invests EVER becoming a problem for solid land in America. But they do prove a point that some of our bloggers are unwilling to see. GW is here to stay.
America isn't the only landmass in hurricane territory.And please lets not start with the global warming discussions.
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Quoting TropicalAnalystwx13:
Opinion/Poll time!

Is 92L Subtropical or Tropical?

A. Tropical

B. Subtropical


Sub-Tropical, hence the appearance
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Quoting sailingallover:

We cannot be looking at the same thing..You are talking about this lopsided dry air intruded upon convectionless wimp?


LOL
but I am with you on that.
I dont see the potential, frankly....
Member Since: October 24, 2005 Posts: 0 Comments: 24883
Opinion/Poll time!

Is 92L Subtropical or Tropical?

A. Tropical

B. Subtropical
Member Since: July 6, 2010 Posts: 113 Comments: 32833
Quoting sailingallover:

We cannot be looking at the same thing..You are talking about this lopsided dry air intruded upon convectionless wimp?

IMO that is Shary.Maybee we don't have the same point of view as you do.But that their is indeed a subtropical storm.
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Quoting MiamiHurricanes09:
You don't seem to understand the difference between a subtropical and a tropical cyclone.


yea that is obvious
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Quoting sailingallover:

We cannot be looking at the same thing..You are talking about this lopsided dry air intruded upon convectionless wimp?

Now youve done it.......YOU hurt 92,s feelings, now it will strengthen and probably hit Bermudi....
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Quoting sailingallover:

We cannot be looking at the same thing..You are talking about this lopsided dry air intruded upon convectionless wimp?



its sub-tropical and yes

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Quoting hydrus:
Here are your pirogues.1...Admin Notice: When using Dr. Masters' blog, please refrain from posting material not relevant to the discussion of tropical weather, or the topic of the blog entry itself. Please do not engage in personal attacks or bickering. Material not conforming to these standards should be flagged with the button and ignored. .........i swear to hair i am just kidding..:)...I couldnt resist. Its been a while since i picked on ya....I feel better now..pfft

:):)
Member Since: October 24, 2005 Posts: 0 Comments: 24883
Quoting sailingallover:

We cannot be looking at the same thing..You are talking about this lopsided dry air intruded upon convectionless wimp?

You don't seem to understand the difference between a subtropical and a tropical cyclone.
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91L still 30 knots, still 1006 mb. 8.0N/52.1W:

AL, 91, 2010102900, , BEST, 0, 80N, 521W, 30, 1006, DB, 34, NEQ, 0, 0, 0, 0, 1009, 200, 120, 0, 0, L, 0, , 0, 0, INVEST, S,
Member Since: November 8, 2009 Posts: 4 Comments: 13802
Quoting washingtonian115:
The 11pm advisory will be interesting.We may see Shary by then I suspect especially with these numbers.
91 t.d at 11...jmo..
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Quoting ackee:
maybe NHC will issue special outlook on 92L tonight upgrading it to shary

We cannot be looking at the same thing..You are talking about this lopsided dry air intruded upon convectionless wimp?

Member Since: September 1, 2009 Posts: 23 Comments: 1007
Quoting pottery:

Cant beat a Pirogue..
Love them.
Here are your pirogues.1...Admin Notice: When using Dr. Masters' blog, please refrain from posting material not relevant to the discussion of tropical weather, or the topic of the blog entry itself. Please do not engage in personal attacks or bickering. Material not conforming to these standards should be flagged with the button and ignored. .........i swear to hair i am just kidding..:)...I couldnt resist. Its been a while since i picked on ya....I feel better now..pfft
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596. JLPR2
Quoting CybrTeddy:
T# for 92L have gone up on the SAB to 2.0.. interestingly enough the SAB thinks 92L's a fully tropical system.


That is well... strange...
Member Since: September 4, 2007 Posts: 7 Comments: 8747
Quoting CybrTeddy:
T# for 92L have gone up on the SAB to 2.0.. interestingly enough the SAB thinks 92L's a fully tropical system.
The 11pm advisory will be interesting.We may see Shary by then I suspect especially with these numbers.
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Quoting brohavwx:
@pottery - They may change their tune when the models bet a better hold on what is happening east or ESE of us (I'm in Barbados).

I find our local met. people don't like to stick their necks out beyond what the NHC is saying, which is not much at this time regarding Invest 91L.

Yet it looks damn impressive.
Good to meet you.
Love yr site, and use it a lot.
Agreed, that area is pretty impressive.
Funny how the Atl. has taken 'front' over the west Carib.
Peculiar times....
Member Since: October 24, 2005 Posts: 0 Comments: 24883
Quoting JLPR2:


As you can tell by the smiley at the end of the question I wasn't actually asking it seriously.
And 92L's % is perfectly fine since the NHC is probably thinking subtropical, the NHC knows what it is doing.

I don't think it has time to go sub tropical..and there is not enough there to go subtropical.
Yes NHC knows what they are doing which is why no one here in the VI's worried about the 3 days of very close to tropical storm weather we got from what became Otto..but we had land slides trees down boats beached again same as the effects of Earl.
91 is a real threat. 92 is pounded flat and surrounded by dry air. Of course you can name anything with a circulation sub tropical..but I don't think it's worth naming..
Member Since: September 1, 2009 Posts: 23 Comments: 1007
591. ackee
maybe NHC will issue special outlook on 92L tonight upgrading it to shary
Member Since: July 15, 2008 Posts: 0 Comments: 1376
Good thinking Potts.
Intelligent life on the planet.
Member Since: July 11, 2006 Posts: 14 Comments: 11423
Quoting TropicalAnalystwx13:


Post #570 :)


Edited.
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Quoting MiamiHurricanes09:
SAB have 92L a T2.0. I think we'll be seeing 20L/Shary tonight.
Maybe 11pm is a good bet?.Just maybe.
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@pottery - They may change their tune when the models bet a better hold on what is happening east or ESE of us (I'm in Barbados).

I find our local met. people don't like to stick their necks out beyond what the NHC is saying, which is not much at this time regarding Invest 91L.

Yet it looks damn impressive.
Member Since: June 3, 2002 Posts: 0 Comments: 64
Quoting Detrina:
anything to be concerned about with that mess in the BoC?
It is suppose to form into a gale center. Probably to much dry air for something tropical..In any case, no circle, no invest, no concern yet..
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T# for 92L have gone up on the SAB to 2.0.. interestingly enough the SAB thinks 92L's a fully tropical system.
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Quoting weatherman12345:
i think we can get 20 named storms

Am with you there, man. Bring on the rain.
Some areas like Jamaica and the Yucatan, northern Mexico have had enough but we here in Florida welcome the cool wet stuff.
It's too dry here for comfort.
Member Since: July 11, 2006 Posts: 14 Comments: 11423
583. JLPR2
Quoting alfabob:


ok, I'll yell it...

EYE! XD
Member Since: September 4, 2007 Posts: 7 Comments: 8747

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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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