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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lots of wind shear on the east coast here i see 70 knots wind shear wow 100 knots wind shear!!!!!
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00Z GFS shows crazy stuffs lol
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Quoting Grothar:
However, the shear tendency could be different. Look at that, I am arguing with myself. Hmmm. Guess I should turn in soon.

moves in tandem with shary as grab by front every thing lifts up and out in sat i notice a low level flow coming off South America preceding area of disturbance and pushing shear against shary forcing her into the front then ne the flow off of S.A. will aide in further dev of 91L
Member Since: July 15, 2006 Posts: 175 Comments: 54827
Quoting KEEPEROFTHEGATE:
a big monsoonal mass of clouds


With an almost complete eyewall and two attached feeder bands. This going off of microwave imagery from a few hours ago, but it looks much more organized now.

Member Since: July 5, 2010 Posts: 0 Comments: 1347
IF shary start moving to the north watch out look at the super wind shear to the north west of her over 80 knots..wow.
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Quoting Grothar:


It looks closer than it actually is. Right now it is just a lot of clouds it looks scary but color enhancement can do that. There will be time.
a big monsoonal mass of clouds
Member Since: July 15, 2006 Posts: 175 Comments: 54827
977. JRRP
Quoting Gearsts:
Shear looks bad but is moving away as 91L moves wnw.Actually shear has been decreasing over 91L with that anticyclone over it.

that is correct
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Quoting jasoniscoolman2010xo:
VERY FAST JET STREAM WINDS OVER 100 MPH OFF THE EAST COAST..NO TROPICAL STORM OR HURRICANE WILL HITT THE USA AT ALL.


Member Since: July 5, 2010 Posts: 0 Comments: 1347
VERY FAST JET STREAM WINDS OVER 100 MPH OFF THE EAST COAST..NO TROPICAL STORM OR HURRICANE WILL HITT THE USA AT ALL.
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we shall see soon hopefully it just fades away that would be nice
Member Since: July 15, 2006 Posts: 175 Comments: 54827
Shear looks bad but is moving away as 91L moves wnw.Actually shear has been decreasing over 91L with that anticyclone over it.
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Quoting alfabob:
Does the NHC plan on warning people when Tomas is making landfall or afterward? Cause its getting pretty close to the first.



It looks closer than it actually is. Right now it is just a lot of clouds it looks scary but color enhancement can do that. There will be time.
Member Since: July 17, 2009 Posts: 71 Comments: 26821
Look at that trough from SE Conus, cleaning the Gom.... that's an expected helping hand....

Member Since: August 2, 2010 Posts: 21 Comments: 9874
However, the shear tendency could be different. Look at that, I am arguing with myself. Hmmm. Guess I should turn in soon.

Member Since: July 17, 2009 Posts: 71 Comments: 26821
Does the NHC plan on warning people when Tomas is making landfall or afterward? Cause its getting pretty close to the first.

Member Since: July 5, 2010 Posts: 0 Comments: 1347
Quoting KEEPEROFTHEGATE:
i don't no which one i like best our scary shary or mighty tomas cause at the moment it looks to be a poss bad storm and iam not scared of shary tomas has me worried looks to come in ne of the first island off trinny


It looks like it could be encountering some strong shear as it moves west or west-northwest.

Member Since: July 17, 2009 Posts: 71 Comments: 26821
NHC data for Isidore - the southernmost altitude for a tropical cyclone in the Atlantic (7.2 N)

Member Since: August 2, 2010 Posts: 21 Comments: 9874
Quoting Grothar:
i don't no which one i like best our scary shary or mighty tomas cause at the moment it looks to be a poss bad storm and iam not scared of shary tomas has me worried looks to come in ne of the first island off trinny
Member Since: July 15, 2006 Posts: 175 Comments: 54827
Quoting Grothar:


What happened to Jackie Guerrido? She seems to stand out more than Susan. Much bigger personality.
She stood out too much, so to speak.
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will tropical storm shary hit bermuda!!! yes or no!!
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Quoting JLPR2:


:O LOL!


What happened to Jackie Guerrido? She seems to stand out more than Susan. Much bigger personality.
Member Since: July 17, 2009 Posts: 71 Comments: 26821
Hurricane Isidore (1990)

Isidore had formed at the southernmost altitude for a tropical cyclone in the Atlantic Basin. Developing near Cape Verde from a tropical wave on September 4, it gradually intensified, becoming a tropical storm on September 5 and a hurricane on September 7. A mid-level trough in the central Atlantic kept it moving northward and it dropped to storm strength for a while before recovering. It was absorbed by an extratropical low north of 50°N on September 17.



Member Since: August 2, 2010 Posts: 21 Comments: 9874
tropical storm Shary
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Member Since: July 17, 2009 Posts: 71 Comments: 26821
Quoting Bordonaro:
948***91L is gonna break ALL the rules and become a TD south of 11N latitude!!!
The formation of tropical cyclones is the topic of extensive ongoing research and is still not fully understood. While six factors appear to be generally necessary, tropical cyclones may occasionally form without meeting all of the following conditions. In most situations, water temperatures of at least 26.5 °C (79.7 °F) are needed down to a depth of at least 50 metres (160 ft); waters of this temperature cause the overlying atmosphere to be unstable enough to sustain convection and thunderstorms. Another factor is rapid cooling with height, which allows the release of the heat of condensation that powers a tropical cyclone.High humidity is needed, especially in the lower-to-mid troposphere; when there is a great deal of moisture in the atmosphere, conditions are more favorable for disturbances to develop. Low amounts of wind shear are needed, as high shear is disruptive to the storm's circulation. Tropical cyclones generally need to form more than 555 kilometres (345 mi) or 5 degrees of latitude away from the equator, allowing the Coriolis effect to deflect winds blowing towards the low pressure center and creating a circulation. Lastly, a formative tropical cyclone needs a pre-existing system of disturbed weather, although without a circulation no cyclonic development will take place.
Member Since: July 15, 2006 Posts: 175 Comments: 54827
958. JLPR2
Quoting sunlinepr:


I just saw Susan in Univision weather news, and she was cool.... She just said that it's a huge wave and that we should be watching it.... But She didn't knew that 92L has already been declared Shary...


:O LOL!
Member Since: September 4, 2007 Posts: 7 Comments: 8747
Quoting jasoniscoolman2010xo:
U ARE 100% RIGHT ABOUT THAT..
i know not where its going but i know where its heading
Member Since: July 15, 2006 Posts: 175 Comments: 54827
Quoting JLPR2:


If that happens Susan will be running all around the studio yelling, Hurricane! XD LOL


I just saw Susan in Univision weather news, and she was cool.... She just said that it's a huge wave and that we should be watching it.... But She didn't knew that 92L has already been declared Shary...
Member Since: August 2, 2010 Posts: 21 Comments: 9874
948***91L is gonna break ALL the rules and become a TD south of 11N latitude!!!
Member Since: August 25, 2009 Posts: 20 Comments: 6785
Member Since: August 2, 2010 Posts: 21 Comments: 9874
Quoting Skyepony:
Shary was a miss.
mayhab but sudden dev could pop up in afternoon heat and humid conditions
Member Since: July 15, 2006 Posts: 175 Comments: 54827
952. JLPR2
Quoting jurakantaino:
Well here we go , even though the models are putting the system passing south it might turn north and cross the islan from Guayam to Isabela in NW


If that happens Susan will be running all around the studio yelling, Hurricane! XD LOL
Member Since: September 4, 2007 Posts: 7 Comments: 8747
Quoting brohavwx:
Okay, 91L will probably fuzz out ... I expect in the morning it will be but a whisp of clouds.

Gone to bed ... later.
When a charter member says it will fuzz out, pay attention
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Quoting CaribBoy:


so it's further north hmm


Seems to be right on track from last 85Ghz scan. Another one should be uploaded within 2-3 hours.
Member Since: July 5, 2010 Posts: 0 Comments: 1347
So now the CMC and the HWRF model doesnt seem so crazy after all.
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Quoting Gearsts:
933. :O WoW thats too far north!


If these coordinates are correct, chances are increased for PR area
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Okay, 91L will probably fuzz out ... I expect in the morning it will be but a whisp of clouds.

Gone to bed ... later.
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T.C.F.A.
INV/91L/XX
MARK
9.83n/51.72w
Member Since: July 15, 2006 Posts: 175 Comments: 54827
Quoting 7544:
red circle at 2am imo


Tomas by 2am. maybe a hurricane some point in the next 24hr imo.
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Quoting KEEPEROFTHEGATE:
T.C.F.A.
INV/91L/XX
MARK
9.83n/51.72w


so it's further north hmm
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Quoting Relix:
91L should miss PR.

;-)


You seem confident, good.
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Quoting Grothar:


Lo entendí la primera vez. LOL

I think if it stays strong you might get a lot of bad weather, but the models have been pretty consistent keeping it more west.
What about the poor souls in Haiti?
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933. :O WoW thats too far north!
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Member Since: July 5, 2010 Posts: 0 Comments: 1347
Member Since: July 5, 2010 Posts: 0 Comments: 1347
Quoting jurakantaino:
Well here we go , even though the models are putting the system passing south it might turn north and cross the islan from Guayam to Isabela in NW


Lo entendí la primera vez. LOL

I think if it stays strong you might get a lot of bad weather, but the models have been pretty consistent keeping it more west.
Member Since: July 17, 2009 Posts: 71 Comments: 26821
937. 7544
red circle at 2am imo
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THE BERMUDA WEATHER SERVICE HAS ISSUED A TROPICAL STORM WATCH FOR
BERMUDA.

SUMMARY OF WATCHES AND WARNINGS IN EFFECT...

A TROPICAL STORM WATCH IN IN EFFECT FOR...
* BERMUDA

FOR STORM INFORMATION SPECIFIC TO BERMUDA...PLEASE MONITOR PRODUCTS
ISSUED BY THE BERMUDA WEATHER SERVICE.


DISCUSSION AND 48-HOUR OUTLOOK
------------------------------
AT 1100 PM AST...0300 UTC...THE CENTER OF TROPICAL STORM SHARY WAS
LOCATED NEAR LATITUDE 27.3 NORTH...LONGITUDE 63.7 WEST. SHARY IS
MOVING TOWARD THE NORTHWEST NEAR 23 MPH...37 KM/HR. A TURN TOWARD
THE NORTH WITH A DECREASE IN FORWARD SPEED IS EXPECTED EARLY
FRIDAY...FOLLOWED BY A TURN TO THE NORTHEAST FRIDAY NIGHT. ON
THE FORECAST TRACK...THE CENTER OF SHARY IS EXPECTED TO PASS NEAR OR
OVER BERMUDA LATE FRIDAY.

MAXIMUM SUSTAINED WINDS ARE NEAR 40 MPH...65 KM/HR...WITH HIGHER
GUSTS. SOME STRENGTHENING IS FORECAST DURING THE NEXT DAY OR SO.

TROPICAL STORM FORCE WINDS EXTEND OUTWARD UP TO 105 MILES...165
KM...TO THE NORTH OF THE CENTER.

ESTIMATED MINIMUM CENTRAL PRESSURE IS 1004 MB...29.65 INCHES.


HAZARDS AFFECTING LAND
----------------------
WIND...TROPICAL STORM CONDITIONS ARE POSSIBLE ON BERMUDA BY FRIDAY
AFTERNOON.

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Quoting Grothar:


Not all of them. The models have been moving further north and more west.


Has visto a estos?

Member Since: July 17, 2009 Posts: 71 Comments: 26821
Quoting KerryInNOLA:
Translate please for us Englishmen. TIA
Quoting Grothar:


que? LOL
Well here we go , even though the models are putting the system passing south it might turn north and cross the islan from Guayam to Isabela in NW
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T.C.F.A.
INV/91L/XX
MARK
9.83n/51.72w
Member Since: July 15, 2006 Posts: 175 Comments: 54827

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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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