An evening shift at NHC: A Shary situation

By: Dr. Jeff Masters , 14:57 GMT le 28 octobre 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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1133. KEEPEROFTHEGATE (Mod)
navy took down 91 l may be upgrade soon
Member Since: 15 juillet 2006 Posts: 174 Comments: 54372
1129. 7544
Quoting stormpetrol:
the lower 48 appears to be closed for business tropically speaking, need i say more!!


and it was also said the area that 91L is in was close for bussiness tooo and look what happen ther lol nothing is set in stone this season see what happens first lol
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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.
agree still got some work to do to be classified. this afternoon it should be alittle more concentrated
Member Since: 11 septembre 2010 Posts: 1 Comments: 4728
Quoting IKE:


Morning low 50.9. Nice with a slight breeze...morning has broken. I'm riding the peace train....


Good tune. I can’t believe it’s been over four decades since I introduced Cat Stevens, Harry Chapin and Neil Diamond to my high school buddies. It seems like only yesterday.
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out now back later, play nice now.
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Pressure down another notch; winds still at 30 knots. Expect classification today. 9.3N/55.7W:

AL, 91, 2010102912, , BEST, 0, 93N, 557W, 30, 1005, DB, 34, NEQ, 0, 0, 0, 0, 1009, 250, 90, 0, 0, L, 0, , 0, 0, INVEST, M,
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1120. KEEPEROFTHEGATE (Mod)
T.C.F.A.
INV/91L/XX
MARK
10.10n/55.23w
Member Since: 15 juillet 2006 Posts: 174 Comments: 54372
1118. roleli
Quoting cat5hurricane:

Exactly. The way I see, why in the hell should they care what gets said on here? Their jobs are not in jeopardy, nor are they competing with some other entity out there. They are the authority. Period. While talk of conspiracy theories may be much more juicy, it's not always the truth. They do their best and do a great job the way I see it.


You are right. The NH are not God. I saw one weather forecaster on a local TV channel in Jamaica talking about Richard. He was so definite about the path Richard would take. I had to say to myself he forgets he is forecaster not God.
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I COULDNT AGREE MORE!
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the lower 48 appears to be closed for business tropically speaking, need i say more!!
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WooooooW!!!!!
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cat5 that image is not of a stong wave but a tropical storm
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1110. roleli
While I have a lot of respect for NHC and great appreciation for the work they do, I wondered, were they caught off-guard with Paula. It went from an Invest to Tropical Storm with 60 MPH winds.

What happened there? Was it just rapid intensification?
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1109. DDR
I'm out
keep you all updated later,im expecting storm warnings to be issued for t&t later today.
Member Since: 27 avril 2007 Posts: 14 Comments: 1702
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.
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Quoting stormwatcherCI:
You are right to a certain extent but the NHC does not issue warnings for the islands and their own mets should be making people aware that there is a very good chance of TS conditions within a certain period of time.
agreed but a lot of mets do get thier info from nhc in the CONUS and make thier call on systems , pleased tht T&T gave warning of 55km winds at least people will know.
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1105. 7544
91l just keeps growing and growing in size as a hurricane symbol look to it . but imo its a ts now . this thing is huge with banding to east and west all around and a tail reaching all the way east to africa this could cover the whole carb if it all stays in tact
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1104. WxLogic
80% by 8AM TWO... close enough to 90% jeje.
Member Since: 14 août 2008 Posts: 4 Comments: 4977
Quoting WxLogic:


I believe there could have been some factors that we're not aware of that could have been delaying the classification.
Everyone says it with each and every possible TC. Most likely waiting to see what recon finds.
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1101. KEEPEROFTHEGATE (Mod)
not advising anybody this sounds like adising to me

REGARDLESS OF DEVELOPMENT...
THIS SYSTEM IS EXPECTED TO BRING LOCALLY HEAVY RAINFALL AND STRONG
GUSTY WINDS TO THE WINDWARD ISLANDS AND NORTHERN PORTIONS OF
VENEZUELA DURING THE NEXT COUPLE OF DAYS
Member Since: 15 juillet 2006 Posts: 174 Comments: 54372
1100. WxLogic
Quoting sailingallover:
I can't believe they didn't bump it last night..and they wasted shary on a potentialess blob
It's had circulation and sustained and organizing convection for a day now


I believe there could have been some factors that we're not aware of that could have been delaying the classification.
Member Since: 14 août 2008 Posts: 4 Comments: 4977
Quoting cat5hurricane:

Exactly. The way I see, why in the hell should they care what gets said on here? Their jobs are not in jeopardy, nor are they competing with some other entity out there. They are the authority. Period. While talk of conspiracy theories may be much more juicy, it's not always the truth. They do their best and do a great job the way I see it.
Yes.
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1098. IKE
Quoting PakaSurvivor:
Morning Ike. Had to break out the sweaters and coats this morning in Crestview. How's your weather?


Morning low 50.9. Nice with a slight breeze...morning has broken. I'm riding the peace train....
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Quoting reedzone:
The islands should be preparing for TS conditions in the next 24 hours. NHC is waiting a tad too long if they don't initiate advisories and warnings by 11 a.m.
The NHC does not issue warnings for the islands. That is up to their own government when they will do that.
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91l the most impressive looking invest this year. and its Almost November!!
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The islands should be preparing for TS conditions in the next 24 hours. NHC is waiting a tad too long if they don't initiate advisories and warnings by 11 a.m.
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Quoting kmanhurricaneman:
yeah they will call it when it almost on top of them, giving the public little time for any final preps, sad sad, most people are not on blogs like us following the weather so they wont know untill the powers to be transmit this info.... aaaaaah boy!!
You are right to a certain extent but the NHC does not issue warnings for the islands and their own mets should be making people aware that there is a very good chance of TS conditions within a certain period of time.
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1092. DDR
Quoting kmanhurricaneman:

what is your local met office saying about 91L

Hi kman,
From the website
ACTIVE TROPICAL WAVE INFORMATION BULLETIN 4

ACTIVE AND VIGOUROUS TROPICAL WAVE 650KM EAST OF
TRINIDAD AND TOBAGO

At 5.00am today the area of low pressure
associated with the very active Tropical Wave is
now centered approximately 650km east of Trinidad
and Tobago and has become better organized.



The wave is moving toward the west to
west-northwest at 24 to 32 kmh and there is a 60%
chance of intensifying into a Tropical Depression
over the next 24 to 48 hours. Environmental
conditions are favourable for further
development.


The leading periphery of the wave should begin
affecting Trinidad and Tobago during the late
afternoon/evening. Moderate to heavy showers can
be expected along with isolated thundershowers
capable of producing 1 to 2 inches of rainfall.
These downpours can yield moderate to severe
street or flash flooding and strong bursts of
gusts in excess of 50kmh.


As the wave continues to intensify and move closer
to Trinidad and Tobago showery activity can yield
3 to 4 inches and possibly 5 to 6 inches from
early Saturday into Sunday. Wind speeds with
gusts in excess of 55kmh are likely.
Member Since: 27 avril 2007 Posts: 14 Comments: 1702
yeah they will call it when it almost on top of them, giving the public little time for any final preps, sad sad, most people are not on blogs like us following the weather so they wont know untill the powers to be transmit this info.... aaaaaah boy!!
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1090. Relix
5PM would be a bit tad lat. Naming it a TD to at least get some warnings out at 11AM is ideal. Gives people, minimum, 6 hours to prepare additionally. Always can come in handy. I expect a TD at 11AM. Just for warnings out. If not... many will be unprepared. Halloween is around the corner.
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Quoting IKE:
Poor NHC gets hammered on here...on the "vent" blog.
Which is very stupid since they are very highly trained and know what they are doing. They can only forecast what they see as they are not God.
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91L up to 80%
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1087. roleli
We in Jamaica will be keeping our eyes on 91L. We have had enough damage from rain associated with Nicole.

The system appears to look much better this morning. I am not surprised NHC upgradde it to 80% chance. I expect it to be higher even a tropical depression at the 11:00 a.m update.
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Morning Ike. Had to break out the sweaters and coats this morning in Crestview. How's your weather?
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1083. KEEPEROFTHEGATE (Mod)


1. A STRONG TROPICAL WAVE LOCATED ABOUT 360 MILES EAST-SOUTHEAST OF THE
SOUTHERN WINDWARD ISLANDS HAS BECOME MUCH BETTER ORGANIZED THIS
MORNING...AND ENVIRONMENTAL CONDITIONS ARE CONDUCIVE FOR A TROPICAL
DEPRESSION OR A TROPICAL STORM TO FORM DURING THE NEXT DAY OR SO.
THERE IS A HIGH CHANCE...80 PERCENT...OF THIS DISTURBANCE BECOMING
A TROPICAL CYCLONE DURING THE NEXT 48 HOURS AS IT MOVES
WEST-NORTHWESTWARD AT 15 TO 20 MPH. REGARDLESS OF DEVELOPMENT...
THIS SYSTEM IS EXPECTED TO BRING LOCALLY HEAVY RAINFALL AND STRONG
GUSTY WINDS TO THE WINDWARD ISLANDS AND NORTHERN PORTIONS OF
VENEZUELA DURING THE NEXT COUPLE OF DAYS. AN AIR FORCE RESERVE UNIT
RECONNAISSANCE AIRCRAFT IS SCHEDULED TO INVESTIGATE THE DISTURBANCE
THIS AFTERNOON.


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: 15 juillet 2006 Posts: 174 Comments: 54372

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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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