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 NRAamy:
Groth..... tres sexy....

;)


Tusen tak!
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Quoting BDADUDE:
Dont be so mean to Grothar. That is very disrespectful!!


Nice to see some young folks who know how to respect their elders. Thanks, BDA.
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Quoting Grothar:
Can't wait for the diurnating tonight? Should be impressive.

are they gonna let ya stay that late i heard lights out by 11 tonight
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380. JLPR2
Quoting sunlinepr:
Levi's prediction is that this monster is going to be stationary S of Haiti.... if that happens, that will be a big shower event for all the area, due to its size.... and it keeps on expanding....




Dang 91L has gotten a little large, at this rate even I might get something from it. :\
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HEH!!
Just in for a moment, before food...
I do wish you all would stop posting images of this Island.
Makes me feel like I am being Observed.

Looks to be a fun time, next few days.
The thing looks kind of dread!
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Groth..... tres sexy....

;)
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Quoting CybrTeddy:
Nice Daguerreotype of Grothar during the Lincoln Admin.

I kid, I kid. :P


YO! LOL
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Just wanted to tell people that if you're in SoFla during the winter, I highly recommend the NHC tour. Did it this year and it was great. For So Flas there's a bonus--the Miami NWS office is there
too and part of the tour. (Don't forget the t-shirts; they're in a little niche in the hallway; mine was $12, cash only, lol).


Link
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Quoting Grothar:
Can't wait for the diurnating tonight? Should be impressive.

The Gulf is looking interesting Gro..
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Quoting EnergyMoron:


double click your avatar.

Pool:

Grother's new avatar

a) Like
b) Dislike



Hey, I got a 9.6. Geez, in those days I thought of myself as a 10. You better hurry with those votes, because I only posted that for Amy. I am going back to my old avatar.
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Nice Daguerreotype of Grothar during the Lincoln Admin.

I kid, I kid. :P
Member Since: July 8, 2005 Posts: 259 Comments: 24548
Levi's prediction is that this monster is going to be stationary S of Haiti.... if that happens, that will be a big shower event for all the area, due to its size.... and it keeps on expanding....


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Quoting EnergyMoron:


double click your avatar.

Pool:

Grother's new avatar

a) Like
b) Dislike



At my age, I can't remember Grother's old avatar 8>)

Guess that disqualifies me.

Regarding 91L, the large size of the general circulation has really gotten my attention. Our last tropical systems have been very small.
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Can't wait for the diurnating tonight? Should be impressive.

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91L is making anxious.....
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18GFS not good for Haiti... but models don't have a good handle of the system yet
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predictions:
90L=30%
91L=60%
92L=70%
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Huh, young Grothar looks like Reed.
Member Since: June 9, 2007 Posts: 4 Comments: 15947
Quoting CaribBoy:

.. and looks like it's gaining latitude....


Tomorrow observations will be decisive in what action to take on the islands....
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Quoting Grothar:


Ha, I am also part Italian. Besides, much taller than Dean and darker. You must be as old as hydrus to remember him.
Me ? old.?..You have as many years on this Earth as I do seconds.
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92L looking better each frame may get classified first as a subtropical storm
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Quoting Grothar:


91L is certainly putting on a show. Looking better in each frame. (By the way, how did you know that was 40 years ago? at my age, that is jut a few)


double click your avatar.

Pool:

Grother's new avatar

a) Like
b) Dislike

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This is bad, real bad, haven't thought I'd see this at least in my lifetime. Maybe, there was something to what was said earlier in the summer. Don't know, but somehow they were on to something like this happening, and now has the time arrived, I don't know, but let us hope not, if you know what I mean, any thoughts?
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Quoting sunlinepr:

.. and looks like it's gaining latitude....
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30-60-30%
Do you Agree???
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Quoting hydrus:
dude..You KNOW i cannot let that one go without a little sumpin ta say.......like its amazing how suddenly 40 years becomes."a few" he he.....Thats it , i am putin up the shuddah,s.


91L is certainly putting on a show. Looking better in each frame. (By the way, how did you know that was 40 years ago? at my age, that is jut a few)
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look at the classic s it has
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Quoting kmanislander:


Hmm. A Viking that looks like James Dean ?? LOL


Ha, I am also part Italian. Besides, much taller than Dean and darker. You must be as old as hydrus to remember him.
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Quoting islander101010:
part of 91 looks like a donut
Just hope it does not cream someone!
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Quoting Grothar:
Happy now Amy. Mind you that picture was taken a few years ago. And no wise cracks, hydrus!
dude..You KNOW i cannot let that one go without a little sumpin ta say.......like its amazing how suddenly 40 years becomes."a few" he he.....Thats it , i am putin up the shuddah,s.
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u mean 91L lol
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91L doing well for DMIN.....
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Impressive

Member Since: June 9, 2007 Posts: 4 Comments: 15947
part of 91 looks like a donut
Member Since: September 11, 2010 Posts: 1 Comments: 4989
Ms. 92 L is looking healthy!!!

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knowing the nhc could be either 50 or 60%
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Quoting 1900hurricane:
Hmm, there apparently is a gunman on my campus armed with an AK47. Not cool...


That's A&M... so far nothing found but shelter in place
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ATLANTIC OBJECTIVE AIDS FOR



DISTURBANCE INVEST (AL912010) 20101028 1800 UTC



...00 HRS... ...12 HRS... ...24 HRS. .. ...36 HRS...

101028 1800 101029 0600 101029 1800 101030 0600



LAT LON LAT LON LAT LON LAT LON

BAMS 7.7N 50.4W 8.4N 54.2W 9.4N 58.0W 10.2N 61.3W

BAMD 7.7N 50.4W 8.2N 53.2W 8.8N 56.0W 9.5N 58.5W

BAMM 7.7N 50.4W 8.3N 53.4W 9.0N 56.5W 9.8N 59.2W

LBAR 7.7N 50.4W 8.7N 53.4W 9.8N 56.3W 11.1N 59.5W

SHIP 30KTS 34KTS 41KTS 49KTS

DSHP 30KTS 34KTS 41KTS 49KTS



...48 HRS... ...72 HRS... ...96 HRS. .. ..120 HRS...

101030 1800 101031 1800 101101 1800 101102 1800



LAT LON LAT LON LAT LON LAT LON

BAMS 10.8N 63.8W 11.2N 68.2W 11.8N 71.9W 12.1N 74.4W

BAMD 10.1N 60.8W 11.5N 65.3W 13.3N 69.7W 14.6N 73.2W

BAMM 10.4N 61.4W 11.5N 65.6W 12.7N 69.6W 13.5N 72.9W

LBAR 12.0N 61.3W 15.7N 64.9W 17.9N 65.1W 17.8N 62.7W

SHIP 60KTS 75KTS 86KTS 95KTS

DSHP 50KTS 70KTS 81KTS 91KTS


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Quoting TropicalMan2010:
50% a comin for 91L
I'd go for 60%.
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Quoting Grothar:


How is that, I just changed it. LOL


Hmm. A Viking that looks like James Dean ?? LOL
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Quoting BDADUDE:
Is that a turtleneck???


No, I just have a short neck! I told you it was an old picture. HA
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Quoting Grothar:


And it's not even Halloween. Not good Keeper, they don't need something like that! Yes, very scary. Never thought I would lived to see a storm that late in October, but then again, if you live over 500 years, you're bound to see a lot. OK, hydrus have fun.
Dont mind if I do. I am used to seeing strong storms late in October, just not in the Eastern Caribbean. Columbus mentioned a fierce October hurricane in his log. Grother probably discussed this storm at length with Christopher back in the 1490,s. By the way Gro, They just came out with Geritol SuperSilver.(trademark). This fantastic new product comes in assorted flavors, so even the intensely old will savor there morning tablet regimen...91 is a bohemoth..
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Quoting Grothar:
Happy now Amy. Mind you that picture was taken a few years ago. And no wise cracks, hydrus!
Is that a turtleneck???
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Quoting KEEPEROFTHEGATE:
lets hope it is just hype but i got to tell yeah i believe 91 l will be scary shary for a halloween nightmare but iam hoping not


The forecast for the Caribbean shows low shear down the road.
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50% a comin for 91L
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91L may go to 50 percent or more on next T W O
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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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