An evening shift at NHC: A Shary situation

By: Dr. Jeff Masters , 28. lokakuuta 2010 klo 14:57 (GMT)

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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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1382. barbados246
29. lokakuuta 2010 klo 15:34 (GMT)
Quoting barbadosjulie:
Heavy rain has begun in Barbados...with periodical high gusts
Hey Julie where in the island are you?
Member Since: 20.05.2010 Posts: 0 Comments: 111
1381. jurakantaino
29. lokakuuta 2010 klo 15:33 (GMT)
Quoting cat5hurricane:

The possibilities are quite broad. The 06Z GFS is taking it near DR.
Or as many of the models show he might reach La Española and take a Lenny turn ENE.... "
Member Since: 31.07.2008 Posts: 0 Comments: 730
1380. barbados246
29. lokakuuta 2010 klo 15:28 (GMT)
Quoting washingtonian115:
Can you belive what the weather channel said in their tropical update?."All is quite in the carribean and rest of atlantic".Do they not see the storm near the lesser antillies?
I'm here in Barbados and we did not know about it either
Member Since: 20.05.2010 Posts: 0 Comments: 111
1379. Seastep
29. lokakuuta 2010 klo 15:26 (GMT)
.
Member Since: 9.09.2008 Posts: 6 Comments: 3412
1378. 1900hurricane
29. lokakuuta 2010 klo 15:26 (GMT)
NEW BLOG!!!!!
Member Since: 2.08.2006 Posts: 45 Comments: 11569
1377. Neapolitan
29. lokakuuta 2010 klo 15:26 (GMT)
NEW BLOG
Member Since: 8.11.2009 Posts: 4 Comments: 13306
1376. Orcasystems
29. lokakuuta 2010 klo 15:25 (GMT)
Quoting kshipre1:
orcasystems,

thanks for this update. please correct me if I am wrong but did the models shown in the graphic take a bit of a westward trend?


From the previous one... no.
The tracks have been shifting a bit more to the north with each run... and the northern turn has been happening earlier.
Member Since: 1.10.2007 Posts: 81 Comments: 26493
1373. 1900hurricane
29. lokakuuta 2010 klo 15:22 (GMT)
From a Microwave standpoint, I've seen many tropical storms with less organization. All we need now is a confirmation of a well defined surface circulation.

Member Since: 2.08.2006 Posts: 45 Comments: 11569
1372. kshipre1
29. lokakuuta 2010 klo 15:21 (GMT)
orcasystems,

thanks for this update. please correct me if I am wrong but did the models shown in the graphic take a bit of a westward trend?
Member Since: 12.07.2010 Posts: 0 Comments: 1130
1371. Stormchaser2007
29. lokakuuta 2010 klo 15:18 (GMT)
2. SUSPECT AREA (APPROACHING WINDWARD ISLANDS)
FLIGHT ONE -- TEAL 71
A. 29/1800Z
B. AFXXX 01KKA INVEST
C. 29/1530Z
D. 09.5N 57.0W
E. 29/1730Z TO 29/2200Z
F. SFC TO 10,000 FT

3. SUCCEEDING DAY OUTLOOK: BEGIN 6-HRLY FIXES ON SYSTEM
NEAR THE WINDWARD ISLANDS AT 30/1200Z NEAR 11N 62W.
Member Since: 9.06.2007 Posts: 4 Comments: 15718
1370. CyclonicVoyage
29. lokakuuta 2010 klo 15:18 (GMT)


Member Since: 30.01.2010 Posts: 0 Comments: 3259
1369. hydrus
29. lokakuuta 2010 klo 15:16 (GMT)
Quoting Orcasystems:


I wouldn't even guess.. but I am surprised none of the Florida wishcasters have not jumped all over it... or said...OMG its might go through box #1 & #2, but the day is early.
Future Tomas will strengthen to cat-5 status moving W-NW and then stall over Miami for a week...j.k...... really..j.k...Looks like Northern South America will see some heavy rain..
Member Since: 27.09.2007 Posts: 1 Comments: 19606
1368. Stormchaser2007
29. lokakuuta 2010 klo 15:16 (GMT)
12z Dynamic.
Member Since: 9.06.2007 Posts: 4 Comments: 15718
1366. hurristat
29. lokakuuta 2010 klo 15:16 (GMT)
Quoting Stormchaser2007:


A fish?

The people of Hispaniola would probably disagree.



Well, don't you know there's no other land besides the CONUS? Everyone else simply lives on makeshift rafts....
Member Since: 15.10.2008 Posts: 11 Comments: 2305
1365. Stormchaser2007
29. lokakuuta 2010 klo 15:15 (GMT)
Member Since: 9.06.2007 Posts: 4 Comments: 15718
1364. Seastep
29. lokakuuta 2010 klo 15:12 (GMT)
ASCAT did update. LLC is at about 8N/58W. Not under the higher level structure. 91L is going to have to build a new LLC, or it will have to jump, imo. Moved from about 7N/54W last night at 8pm EDT to about 8N/58W at 9am EDT this morning. Not definitive with the new ASCAT, but that's my take.

Last night



This morning

Member Since: 9.09.2008 Posts: 6 Comments: 3412
1363. SherwoodSpirit
29. lokakuuta 2010 klo 15:12 (GMT)
Quoting Neapolitan:
To those second-guessing the NHC, you should write to tell them you want to see more of the mets there doing this:



Bahaha! Good one.
Lucky thing I swallowed the sip of coffee I just took before I saw that. Nearly had to clean my monitor.
Member Since: 18.07.2006 Posts: 0 Comments: 392
1361. Orcasystems
29. lokakuuta 2010 klo 15:11 (GMT)
Quoting reedzone:


Your being a bit childish, I was just giving my two cents on the invest.


Check the time.. I posted it about the same time you did... I don't even see yours.. it was meant in humour. If you take stuff to seriously.. you'll go nuts.
Member Since: 1.10.2007 Posts: 81 Comments: 26493
1360. Stormchaser2007
29. lokakuuta 2010 klo 15:10 (GMT)
Just by looking at visible you can see that its still pretty broad.

Member Since: 9.06.2007 Posts: 4 Comments: 15718
1359. reedzone
29. lokakuuta 2010 klo 15:10 (GMT)
Quoting Orcasystems:


I have no idea where its going.... did anyone call and ask Reed???


Your being a bit childish, I was just giving my two cents on the invest.
Member Since: 1.07.2008 Posts: 13 Comments: 7334
1357. Orcasystems
29. lokakuuta 2010 klo 15:07 (GMT)


I have no idea where its going.... did anyone call and ask Reed???
Member Since: 1.10.2007 Posts: 81 Comments: 26493
1356. JRRP
29. lokakuuta 2010 klo 15:07 (GMT)
Member Since: 16.08.2007 Posts: 0 Comments: 5085
1355. ILwthrfan
29. lokakuuta 2010 klo 15:05 (GMT)
91L is not going to be anything until he can get a decent LLC developing, along with any type of CDO development to with it. As of right now his upperlevel atmoshpere is very impressive but his bark is worse than his bite, until he tightens up that circulation. This is a very large storm.
Member Since: 2.02.2010 Posts: 0 Comments: 1403
1354. reedzone
29. lokakuuta 2010 klo 15:05 (GMT)
Looks like 91L will win out of the shear, the anticyclone still attached to it, shoving the high wind shear that everyone thought (including me) would hamper intensification until it reached the Western Caribbean. I see no reason, if the shear continues to move out of the way, for 91L to become a Hurricane, but that is a long shot. It all depends if the anticyclone hangs around for a while, which is looking likely, but we'll see.
As far as the track goes, it's late October and Novemeber, for those who really think this will make it to the Western Caribbean, are you serious?? My two cents is that it will slow down south of the Islands and do an Omar (2008). Although the EURO has a totally different scenario, which is possible. Misses the troughs, but the storm would have to be weak, which is not panning out well enough for that solution to verify, it's possible though. There are possibilities, but we can't really pinpoint an actual path yet.
Member Since: 1.07.2008 Posts: 13 Comments: 7334
1353. NRAamy
29. lokakuuta 2010 klo 15:03 (GMT)
SQUAWK!!!!!
Member Since: 24.01.2007 Posts: 316 Comments: 31944
1352. Orcasystems
29. lokakuuta 2010 klo 15:03 (GMT)
Quoting Floodman:


That's me: professional buzzkill!

On the serious side, future Tomas (and I hate saying that, but damn, look at him...barring something truly unforeseen he'll be named soon enough) Looks very good this morning, but where he's headed? 6-5 and pick'em at this point


I wouldn't even guess.. but I am surprised none of the Florida wishcasters have not jumped all over it... or said...OMG its might go through box #1 & #2, but the day is early.
Member Since: 1.10.2007 Posts: 81 Comments: 26493
1351. Stormchaser2007
29. lokakuuta 2010 klo 15:03 (GMT)
Pretty broad core.

Should take 6-24 hours to tighten up.

Member Since: 9.06.2007 Posts: 4 Comments: 15718
1348. Neapolitan
29. lokakuuta 2010 klo 15:00 (GMT)
Quoting P451:


Bust? I rarely saw any competent posters claim that.

Oh, there were many. Just for fun, I went back and looked at a few predictive comments from late August. These are all from current, well-known forum members:

"I think...a busy season is becoming more unlikely...the Models are forecasting very little activity over the next 2 weeks. The GFS show a winter time like storm in the north atlantic at 230 hours...that will through things off for a while in the MDR...could be a weak season..."

"i have reduced numbers to 12 to 14 for a total and its looking more and more like thats what it will be we have had 5 systems 3 with names 1 cane that leaves another 10 or 11 for the sesaon which will be 13 14 in total"

"I want to take a momemt to apologize to XXXXXX.. Earlier in the season I thought that he was off his rocker, downplaying development with all of these earlier systems. As the season has progressed, he has proven to be RIGHT in downcasting, and most of the rest of us around here were wrong about all the previous systems. We will be lucky to get 11 or 12 (10 seems more likely) named systems..."

"The numbers are set too high. I'm doubting it achieves my forecast of 13."

"Maybe we end the season with 11 to 13 storms the most. Just guessing after 52 years of experience living in the caribbean."

Of course, no ridicule is intended (that's why I've omitted the names). I merely bring these up to highlight the dangers inherent in long-term forecasting, especially when done by rank amateurs, which the majority of us--myself included--most definitely are. And things could certainly have gone the other way--that is, as those who engaged in baseless and illogical nowcasting by predicting an inactive season thought--meaning that we who agreed with both the science and the experts' higher numbers would be the ones sitting here instead of them just a few months later, preparing to eat our heapin' platefuls of crow forkful by cold, feathery forkful.

Whew... ;-)
Member Since: 8.11.2009 Posts: 4 Comments: 13306
1346. Stormchaser2007
29. lokakuuta 2010 klo 14:58 (GMT)
Quoting weatherlover94:
i guess it is possible that this one could become a fish on us after i hits the virgin islands and all them places who knows


A fish?

The people of Hispaniola would probably disagree.

Member Since: 9.06.2007 Posts: 4 Comments: 15718
1343. JRRP
29. lokakuuta 2010 klo 14:57 (GMT)
1005 mb
Member Since: 16.08.2007 Posts: 0 Comments: 5085
1342. weatherlover94
29. lokakuuta 2010 klo 14:56 (GMT)
i guess it is possible that this one could become a fish on us after i hits the virgin islands and all them places who knows
Member Since: 8.09.2010 Posts: 0 Comments: 1820
1341. Floodman
29. lokakuuta 2010 klo 14:55 (GMT)
Quoting Orcasystems:


Now stop that... you know better then to ruin the kids fun with facts and logic.


That's me: professional buzzkill!

On the serious side, future Tomas (and I hate saying that, but damn, look at him...barring something truly unforeseen he'll be named soon enough) Looks very good this morning, but where he's headed? 6-5 and pick'em at this point
Member Since: 2.08.2006 Posts: 10 Comments: 9922
1339. JRRP
29. lokakuuta 2010 klo 14:54 (GMT)
loosing convection but nice structure
Member Since: 16.08.2007 Posts: 0 Comments: 5085
1338. Orcasystems
29. lokakuuta 2010 klo 14:54 (GMT)
Quoting weatherlover94:


i dont know why the models have this thing going w for a while then out to sea


My guess would be steering currents.
Member Since: 1.10.2007 Posts: 81 Comments: 26493
1337. Stormchaser2007
29. lokakuuta 2010 klo 14:52 (GMT)
Tough call.

Member Since: 9.06.2007 Posts: 4 Comments: 15718
1336. weatherlover94
29. lokakuuta 2010 klo 14:52 (GMT)
Quoting Orcasystems:
Complete Update



AOI
AOI AOI AOI

AOI AOI AOI

TS BUSTED FORECAST ALIBI


i dont know why the models have this thing going w for a while then out to sea
Member Since: 8.09.2010 Posts: 0 Comments: 1820
1335. Seastep
29. lokakuuta 2010 klo 14:52 (GMT)
The ASCAT from lat night showed that the LLC was way S, very close to S. America. Could have jumped N, of course.

The large cloud cover and pattern is in the higher levels and more related to the upper level ridge on top, giving it that nice appearance. Where the LLC is, is anyone's guess, but we will know soon enough when the HH get out there. Doubt ASCAT updates before then.

Link

Member Since: 9.09.2008 Posts: 6 Comments: 3412
1334. Floodman
29. lokakuuta 2010 klo 14:51 (GMT)
Quoting pottery:

Yeh!
But standing on chairs and screaming is much more fun, than sitting and waiting.
Get loose, man!
heheheheh


I want to party with you, cowboy! How's things, pot, my friend?
Member Since: 2.08.2006 Posts: 10 Comments: 9922
1333. wunderkidcayman
29. lokakuuta 2010 klo 14:51 (GMT)
I guess no advisorys for 91L yet
Member Since: 13.06.2009 Posts: 2 Comments: 9598

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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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