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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Member Since: Posts: Comments:
HYDRUS PLEASE REMOVE MY QUOTE
Member Since: July 15, 2006 Posts: 173 Comments: 54344
when the residents of the lesser antilles were getting relax to the end of the atlantic season, here comes a pertabation from the itcz which is at their doorsteps with the likely hood of a named storm the next 24-48 hrs. as of a few satelite frames within the last hour, 91L is growing in organisation. although there is no surface reflection at the moment and the latest ASCAT does not show any closed low. there however is a vigorous mid level circulation which at the moment is beginning to take a wnw track.the steering currents from Penn State e wall shows this motion for the next 48hrs. the structure of 91L lookes very impressive and one can see some bandind which is indicarive of a surface low trying to form. nomatter what happens this system will bring hravy rains and gusty winds to Trinidad and as far north to martinique. residents of trinidad to as far as martinique should monitor the progess of this developing disturbance
Member Since: Posts: Comments:
Quoting RufusBaker:
This could be the mighty storm of Nov in the gulf
Why do you think 91L would go that far west?
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Looks like is true that when Jeff goes on vacation that the tropics tend to heat up... Doc is technically on vacation you could say at NHC.
Member Since: August 14, 2008 Posts: 4 Comments: 4977
XX/XX/AOI
Member Since: July 15, 2006 Posts: 173 Comments: 54344
Quoting Hurricanes101:


look at his name, he is a troll
Figures.I wasn't really paying attention to his name.I just saw the rude post he made.
Quoting gordydunnot:

Boy their giving this on a hard time 30% ???
It's getting that s shape.
Member Since: Posts: Comments:
Quoting TropicalMan2010:
heres what i see with 91L right now...

Tropicalman, amazing graphics!
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This could be the mighty storm of Nov in the gulf
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Boy their giving this one a hard time 30% ???
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T.C.F.A.
INV/92L/XX
MARK
27.17N/60.63W
Member Since: July 15, 2006 Posts: 173 Comments: 54344
POSS T.C.F.A.
INV/91L/XX
MARK
8.58n/50.28w
Member Since: July 15, 2006 Posts: 173 Comments: 54344
265. DDR
Good evening all
I will give you all updates as 91L appraoches,no doubt pottery will do the same
Member Since: April 27, 2007 Posts: 14 Comments: 1701
Quoting washingtonian115:
Thats not very nice.And these so called "geeks" save lives.Just so you know....


look at his name, he is a troll
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Quoting CycloneOzAteMyBaby:
The NHC looks just like I had envisioned it.

Plenty of geeks with a smattering of fatties.
Thats not very nice.And these so called "geeks" save lives.Just so you know....
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STAY AWAY FROM BONAIRE! 16 days :)
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Quoting sunlinepr:
Yep.Looks like we may have an organizing system down their.And I'm glad your enjoying your time down at the NHC Doc.
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cats acting wierd we are doomed slu around?
Member Since: September 11, 2010 Posts: 1 Comments: 4724
if it stays off s America i think thats northern s america then this thing could be the strongest storm the carribian has seen so far this year and i do think this one has the potential to hit the us
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Lots of volcanic activity, Russian Volcanoes going up, some up to 35,000 foot ash clouds.

Link
Member Since: Posts: Comments:
Member Since: Posts: Comments:
92 seems to be moving west just north of a ull
Member Since: September 11, 2010 Posts: 1 Comments: 4724
hey folks glad to be back with you just havent had time to get on look at invest 92 L the ship models shows a big cat 2 with 105 mph winds at the end of the model run....what will it do? go into mexico like the rest or threaten the us? any thoughts
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Member Since: Posts: Comments:
Good afternoon everyone

I have been off the blog for a couple of days during the slow period but it looks like there may some action in the offing soon with 91L.

I also noticed that the CIMSS steering layer map that used to cover the Caribbean no longer does so. Anyone have any info why that is and whether the Caribbean is no longer being included for some reason ??

TIA
Member Since: Posts: Comments:
Quoting SouthDadeFish:
Not sure if it has been posted yet, but:

28/1745 UTC 8.7N 50.7W T1.5/1.5 91L -- Atlantic


That's a nice jump up from from too weak.


It's also further NORTH
Member Since: October 6, 2007 Posts: 0 Comments: 6229
91L looks so ominous
Member Since: October 6, 2007 Posts: 0 Comments: 6229
Not sure if it has been posted yet, but:

28/1745 UTC 8.7N 50.7W T1.5/1.5 91L -- Atlantic


That's a nice jump up from from too weak.
Member Since: Posts: Comments:
Quoting pottery:

A good Barbados site-
www.brohavwx.com


Many links to explore.... for my bookmarks collection....
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Quoting TOMSEFLA:
levi update today?


Friendly advice: check the member blogs for recent updates (top of every page under Blogs).

Link
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Quoting pottery:

A different kind of Jig, I had in mind!


I'd hope so :P
Member Since: October 15, 2008 Posts: 11 Comments: 2312
BBL
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239. 7544
91L might have a holloween costume on looks like a coma shape hurricane in apperance lol
Member Since: May 6, 2007 Posts: 0 Comments: 6855
Quoting sunlinepr:

Caribbean Disaster Emergency Management Agency

Link


Grenada Met. Office
Link

A good Barbados site-
www.brohavwx.com
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Quoting hurristat:


In the long run, .7 is only about 60 miles...

Storms have been known to influence South America
Here is the low six days out...
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Quoting NRAamy:
check check check.... 1 2 3....




Looks good here...
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Quoting pottery:

That's good.
But enter 'piarco' in the search box, top of this page, for a preferred site.


Thanks for that...
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Caribbean Disaster Emergency Management Agency

Link


Grenada Met. Office
Link
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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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