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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1283. hydrus
Quoting CyclonicVoyage:
I think that's the best looking invest I've ever seen in my lifetime.
The NCEP has Haiti getting the worst of it..Link Cannot get the link to work..It shows the storm moving slowly right across the middle of the island.
Member Since: September 27, 2007 Posts: 1 Comments: 20501
kshipre1 I think that 91L will move south of Jamaica and recurve near the Caymans and into central Cuba and Central Bahamas
Member Since: June 13, 2009 Posts: 2 Comments: 11004
Quoting pottery:

Well, it's just settin' there. Sort of waiting to see what happens next.

If the tree drives away in your auto, RUN!!
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I bet you the doc is busy at the NHC right now.With almost two storms going on at once.
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1279. ryang
Starting to rain here in Barbados. Few gusts in squalls.
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1278. pottery
Quoting washingtonian115:
As we've all said this season hasn't really been normal.

Nore have some of the Posters on here!
LOL
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1277. pottery
Quoting Bordonaro:

Good morning! The Calabash tree finish it's TC preparations yet??

Well, it's just settin' there. Sort of waiting to see what happens next.
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1276. Jax82
SST's



TCHP

Member Since: September 2, 2008 Posts: 1 Comments: 1261
Quoting RitaEvac:
This image could pass for an August/September day in the tropics

As we've all said this season hasn't really been normal.
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Quoting pottery:
Good (?) Morning all.
91L is pretty this morning.
Nice weather here, with strong NE winds moving the clouds across the otherwise blue sky.
Actually clouding up a little more now..
Models showing more northward track today than before.
I dont think that is a good thing. Rotation can only improve as it gets north, Resulting in strengthening to the detriment of the Islands.

Good morning! The Calabash tree finish it's TC preparations yet??
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1273. hydrus
Quoting RitaEvac:
This image could pass for an August/September day in the tropics

very true.
Member Since: September 27, 2007 Posts: 1 Comments: 20501
1272. pottery
Quoting CyclonicVoyage:
I think that's the best looking invest I've ever seen in my lifetime.

Agree with that!
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1271. hydrus
Quoting Bordonaro:

"91L" is trick or treating as a dog!!
A very big dog....And somewhere in the Caribbean is a bone to be chewed.
Member Since: September 27, 2007 Posts: 1 Comments: 20501
1270. pottery
Good (?) Morning all.
91L is pretty this morning.
Nice weather here, with strong NE winds moving the clouds across the otherwise blue sky.
Actually clouding up a little more now..
Models showing more northward track today than before.
I dont think that is a good thing. Rotation can only improve as it gets north, Resulting in strengthening to the detriment of the Islands.
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This image could pass for an August/September day in the tropics

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reed,

any chance you see of 91L moving futher westward instead of recurving near eastern cuba?

I am assuming the High above will not be that strong
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Quoting hydrus:
91L has a tail.

"91L" is trick or treating as a dog!!
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I think that's the best looking invest I've ever seen in my lifetime.
Member Since: January 30, 2010 Posts: 0 Comments: 3259
1264. Relix
91L should miss PR by a nice margin. Some good rainy days though!
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1263. hydrus
91L has a tail.
Member Since: September 27, 2007 Posts: 1 Comments: 20501
1262. hydrus
Member Since: September 27, 2007 Posts: 1 Comments: 20501
According to the NHC's climatology page:

--The 10th named storm of an average season forms on November 23, while the 11th (when there is one) appears on November 23. This year's tenth named storm, Julia, formed on 9/12, while number eleven, Karl, formed on 9/14.

--The fifth hurricane of an average season forms on forms on October 7, while the eighth (when there is one) appears on November 23. This year's fifth hurricane, also Julia, formed on 9/12, while number six--again, Karl--formed on 9/14.

--The first major hurricane of an average season forms on forms on September 4, while the second (when there is one) appears on October 3. This year's first major, Danielle, formed on 8/22, while number two, Earl, formed on 8/25.

More facts:

--The letter 'S' has only been used twice before in naming a storm: 1995's Sebastien--a tropical storm that formed on 10/21--and 2005's Stan, a hurricane that appeared on October 2. (FWIW, both previous 'S' storms had male names, so Shary is the first "female" 'S' storm.)

--Assuming 91L makes it to 'Tomas'--which appears very likely at the moment, it'll be only the third time the letter 'T' was reached: Hurricane Tanya, which formed on 10/27, was the last storm of 1995, while 2005's TS Tammy formed on October 5. (And again FWIW, both previous 'T' storms had female names, so Tomas would be the first "male" 'T' storm.)

--If all storms had been named under the current naming scheme, 1969 would have reached the letter 'S' on November 21; there would have been no 'T' storm.
Member Since: November 8, 2009 Posts: 4 Comments: 13457
Quoting jfthurrican:
LOS MODELOS ESTAN MUY EN DESACUERDO ESTA MUY IMPREDECIBLE 91L.
QUE PODRIAMOS ESPERAR LOS DE LAS HISPANIOLA???


While I think that the public should be informed of 91L, I wouldn't start worrying for Haiti quite yet...
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Someone in Carribean is gonna get plastered..Shields still up for Florida tho.
Member Since: July 25, 2006 Posts: 0 Comments: 551
I hope Tomas takes the Mona Passage than a straight NE pathway away from most populated areas.
Member Since: June 16, 2005 Posts: 0 Comments: 1205
Quoting Grothar:


Most models are keeping it South of PR except for the HWRF. The other models want to keep it more west then a turn to the North around Hispanola later. Until they know the speed and strength, it will be very hard to predict direction.
Hispanola doesn't need another disater.They've already had a deadly one back in january.Stay away 91L.Your company isn't needed.
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Quoting cat5hurricane:

Yep

And there there was Tomas :O)!!
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1252. Jax82
when was the last time Barbados was hit with a storm near Halloween?
Member Since: September 2, 2008 Posts: 1 Comments: 1261
1250. Grothar
Quoting washingtonian115:
Oh my.Thats not looking to good for Puerto Rico.And I will say this about 91L.I think it's very well on the verge of becoming our next storm.I think the nhc will upgrade it possibly when the hh get in their.Like we saw with other storms this year.


Most models are keeping it South of PR except for the HWRF. The other models want to keep it more west then a turn to the North around Hispanola later. Until they know the speed and strength, it will be very hard to predict direction.
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91l,shoud be a td@11am,no way in heck is their enough sustained convection around the cnter yet for a ts,max winds the antilies wind should be no higher than 50mph thru 48hrs,aftr 48hrs could get much strongr when its south of pr..jmo
Member Since: October 5, 2007 Posts: 20 Comments: 4970
Heavy rain has begun in Barbados...with periodical high gusts
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1247. Grothar
Quoting jfthurrican:
LOS MODELOS ESTAN MUY EN DESACUERDO ESTA MUY IMPREDECIBLE 91L.
QUE PODRIAMOS ESPERAR LOS DE LAS HISPANIOLA???


Most are in agreement but not on strength.
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Quoting Grothar:
Oh my.Thats not looking to good for Puerto Rico.And I will say this about 91L.I think it's very well on the verge of becoming our next storm.I think the nhc will upgrade it possibly when the hh get in their.Like we saw with other storms this year.
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I say this I am not trusting most of the models at all but I do with the XTRP and yes I know it's not a model
Member Since: June 13, 2009 Posts: 2 Comments: 11004
Where are the HH's flying out of today en route to 91L?
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LOS MODELOS ESTAN MUY EN DESACUERDO ESTA MUY IMPREDECIBLE 91L.
QUE PODRIAMOS ESPERAR LOS DE LAS HISPANIOLA???
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interesting to see the cone or trajectory of this system going to be some heavy rains in that region 8 inches?
Member Since: September 11, 2010 Posts: 1 Comments: 4329
JRRP they are replacing 91L to 21L
Member Since: June 13, 2009 Posts: 2 Comments: 11004
1239. Grothar
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I thinking it'll go straight to "Thomas".
We've seen a lot less impressive-looking systems designated. JMHO.
Member Since: July 25, 2006 Posts: 0 Comments: 551
Quoting cat5hurricane:

Yep


It's best that they do because it is too close to the islands, they need to be aware of how much bigger then situation is. I expect watches and warnings to be out.
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1236. Grothar
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Quoting HaboobsRsweet:
The signs were easy to see last night why it was not named a TD. The center was way to broad and convection was disorganized. This morning it looks a lot better but the center is still broad. This means the winds are not nearly as high as you think. It will get its status today as it improves. The mets down there suck if they are waiting to tell people that a system that has signs of being a tropical system will hit in the next couple of days.

NHC does a great job with the tools they had. It is easy to sit here and make a call but look in the mirror. How many times are you wrong? Yea way more than they are. A lot of people on here would have had Tampa evacuated and costing millions if they worked at NHC for Richard.
..agreed looks more like a monsoonal low pressure we'd find in the westpac,this season is starting to make less and less sense,our gov is messing w/the wx patterns and the consequences will be irreversable and extreme imo
Member Since: October 5, 2007 Posts: 20 Comments: 4970

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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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