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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1232. Grothar
Quoting kmanhurricaneman:
grothar stop freaking out puerto Rico


Lo sentimos!
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It appears the NAVY pulled 91L and is renumbering it to 21L. Looks like the NHC will pull the trigger at 11 a.m.
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1229. Grothar
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Wow! Just got on and 91L sure looks like it should already have a name, IMO!

Morning folks!
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grothar stop freaking out puerto Rico
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1226. hydrus
Quoting Skyepony:
Jakarta - Rescue workers were racing against time Friday in their search for hundreds of people missing on Indonesia's tsunami-hit Mentawai islands as an official estimated that the death toll could rise to around 600.

The confirmed death toll from Monday's tsunami and magnitude-7.7 earthquake rose to 408 people while 303 people were listed as missing, said the Regional Disaster Management Agency in West Sumatra province, where the Mentawais are located. At least 44 people were reported injured.

Storms and waves as high as 6 metres have prevented aid from reaching some areas in the Mentawai chain, said Ade Edward, head of the agency.

Edward estimated that only about 100 of the missing were still alive.

"We are assuming that one-third of the missing are in the hills but have not been accounted for by local officials," he said.

"The others were perhaps swept away by the sea or buried under the mud," he added. more....
That area has been receiving more than its fair share of disasters. I pray they will have some tranquility some day. It is a beautiful part of the world. And very dangerous...
Member Since: September 27, 2007 Posts: 1 Comments: 22624
1225. JRRP
Quoting KEEPEROFTHEGATE:
awaiting re-number

ok
Member Since: August 16, 2007 Posts: 0 Comments: 6213
1224. Grothar
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1223. Grothar
Dynamic models:

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1222. KEEPEROFTHEGATE (Mod)
Quoting JRRP:
Link
where is 91L ???
awaiting re-number
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puerto Rico!!! what uuuup!!!!!
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1218. JRRP
Quoting hurristat:


that may be hard to do if the population isn't aware something is out there... onamet should send out some public notices or something like that...


jejeje is true
Member Since: August 16, 2007 Posts: 0 Comments: 6213
1217. JRRP
Link
where is 91L ???
Member Since: August 16, 2007 Posts: 0 Comments: 6213
1215. beell
91L just needs to gain a little more latitude to pull together.
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Quoting JRRP:

la onamet le esta dando especial seguimiento y exhorta a la poblacion mantenerse atentos


that may be hard to do if the population isn't aware something is out there... onamet should send out some public notices or something like that...
Member Since: October 15, 2008 Posts: 11 Comments: 2312
I do see what Neo is saying with the extremely intense convection limited to the curve band, but I do think that this will be a depression or possibly a storm later today. Outflow is excellent in the Western quadrants and convection will only be increasing.


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1212. Skyepony (Mod)
Jakarta - Rescue workers were racing against time Friday in their search for hundreds of people missing on Indonesia's tsunami-hit Mentawai islands as an official estimated that the death toll could rise to around 600.

The confirmed death toll from Monday's tsunami and magnitude-7.7 earthquake rose to 408 people while 303 people were listed as missing, said the Regional Disaster Management Agency in West Sumatra province, where the Mentawais are located. At least 44 people were reported injured.

Storms and waves as high as 6 metres have prevented aid from reaching some areas in the Mentawai chain, said Ade Edward, head of the agency.

Edward estimated that only about 100 of the missing were still alive.

"We are assuming that one-third of the missing are in the hills but have not been accounted for by local officials," he said.

"The others were perhaps swept away by the sea or buried under the mud," he added. more....
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1210. JRRP
Member Since: August 16, 2007 Posts: 0 Comments: 6213
1208. Skyepony (Mod)
UK coast guard: Polish tall ship loses both masts in severe weather, 36 teenage sailors aboard
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1207. hydrus
Quoting Neapolitan:
I see a lot of the standard armchair mets here yet again this morning second-guessing the experts. I should be used to it by now; the conspiracy theorists, the anti-NHC'ers, the HAARP players--all of them claiming to know more than a widely-dispersed group of very talented meteorologists, many who've spent more years looking at hurricanes professionally than some of those here complaining have even been on earth...and that's not to mention their combined decades of advanced schooling leading to numerous doctoral degrees.

sigh...

Guys, there's one solid reason the NHC has not yet classified 91L as a TD or a TS: it's not one yet. Period. And when it is, they will.
Great post....Excellent post.....Really good post....Terrific post.....91L has what appears to be a significant tail..
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1204. JRRP
GFDL
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1202. KEEPEROFTHEGATE (Mod)
Quoting jasoniscoolman2010xo:
very high wind shear will kill TROPICAL STORM SHARY soon. OVER 60 KNOTS wwe say goodbye to shary..high wind shear will eat shary for lunch soon.
just as its forecasted to do
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Quoting Neapolitan:
An hour ago, ATCF said 91L's CoC was at 9.3N/55.7W. While satellite presentation looks great on RGB and visible, rainbow IR tells a slightly different story. Mainly, there seems to be a lack of convection right at the center, with the majority of the heavy stuff many miles to the north and east. I'm not saying this won't develop; it appears very robust for a mere disturbance. I'm also not saying the NHC won't reclassify it this morning, especially given its proximity to the islands. But, while I'm definitely no expert, it doesn't look to me quite like a TD just yet...and certainly not a TS.

As always, of course, I could be proven wrong...


I definitely disagree....
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I think that Haiti and south Bahamas will be safe from this one but I think it will be hell for us here in the Cayman Islands and in Jamaica and in Central Cuba and Central Bahamas
Member Since: June 13, 2009 Posts: 2 Comments: 12716
Here's a good reason why this is taking so long to name...(advisory from the tropical depression that became wilma)

Quoting NHC:
BOTH TAFB AND SAB CAME IN WITH A DVORAK SATELLITE INTENSITY ESTIMATE OF T2.5/35 KT. HOWEVER ...OFTENTIMES THE SURFACE WIND FIELD OF LARGE DEVELOPING LOW PRESSURE SYSTEMS LIKE THIS ONE WILL LAG ABOUT 12 HOURS BEHIND THE SATELLITE SIGNATURE. THEREFORE... THE INITIAL INTENSITY HAS ONLY BEEN INCREASED TO 30 KT


this is quite applicable here
Member Since: October 15, 2008 Posts: 11 Comments: 2312
An hour ago, ATCF said 91L's CoC was at 9.3N/55.7W. While satellite presentation looks great on RGB and visible, rainbow IR tells a slightly different story. Mainly, there seems to be a lack of convection right at the center, with the majority of the heavy stuff many miles to the north and east. I'm not saying this won't develop; it appears very robust for a mere disturbance. I'm also not saying the NHC won't reclassify it this morning, especially given its proximity to the islands. But, while I'm definitely no expert, it doesn't look to me quite like a TD just yet...and certainly not a TS.

As always, of course, I could be proven wrong...
Member Since: November 8, 2009 Posts: 4 Comments: 13800
1195. KEEPEROFTHEGATE (Mod)
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Here in Dom.Rep. we are watching pretty close 91L, looks impressive but hopefully it's moving W and (I Think) will pass south from this island as we can see in the animated loop.LINK: http://www.ssd.noaa.gov/goes/east/carb/flash-jsl.html
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1192. KEEPEROFTHEGATE (Mod)
ALERT ATCF MIL 91X XXX 101029120000
2010102912
7.5 306.0
9.2 302.4
100
7.5 306.0
291200
1010291200
1
SUBJ/TROPICAL CYCLONE FORMATION ALERT//
WTNT21 KNGU 291200
RMKS/1. FORMATION OF A SIGNIFICANT TROPICAL CYCLONE IS POSSIBLE WITHIN
100 NM EITHER SIDE OF A LINE FROM 7.5N 54.0W TO 9.2N 57.7W WITHIN
THE NEXT 12 TO 24 HOURS. AVAILABLE DATA DOES NOT JUSTIFY IS-
SUANCE OF NUMBERED TROPICAL CYCLONE WARNINGS AT THIS TIME.
2. CURRENT MODEL GUIDANCE IS DEPICTING INTENSIFICATION OF A LOW
SITUATED APPROXIMATELY 600 MILES ESE OF THE LEEWARD ISLANDS, MOVING
WEST-NORTHWEST AT APPROXIMATELY 15-20 KTS. THIS SYSTEM IS MOVING
WEST UNDER AN UPPER LEVEL RIDGE AND LOW LEVELS OF WIND SHEAR WHICH,
ALONG WITH WARM SEA SURFACE TEMPERATURES, WILL HELP TO ENHANCE THE
DEVELOPMENT OF THIS TROPICAL FEATURE.
3. REMARKS: THIS ALERT WILL BE REISSUED, UPGRADED TO A WARNING OR
ALLOWED TO EXPIRE BY 301200Z.//
9110073106 88N 329W 20
9110073112 89N 335W 20
9110073118 90N 341W 20
9110080100 92N 347W 20
9110080106 94N 353W 20
9110080112 96N 358W 25
9110080118 98N 366W 25
9110080200 101N 374W 25

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1189. Skyepony (Mod)
Wunder how much that storm the other day is going to cost..

$95 million approved for storm relief in Iowa for the storms they had in June, July & August earlier this year.
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Quoting KEEPEROFTHEGATE:
init will be TD 21L then during or after recon TS Tomas i reckon


Thank you!
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1186. KEEPEROFTHEGATE (Mod)
Quoting P451:
mighty tomas
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Quoting CyclonicVoyage:


I surely don't agree with you there. Saying anyone is out of the woods at this point is rather foolish.

Did Richard not school the best of them?


Yes richard has been a nightmarre to predict. However it's not possible to say with precision which area will be affected after the windwards.
Member Since: October 6, 2007 Posts: 0 Comments: 6455

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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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