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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583. JLPR2
Quoting alfabob:


ok, I'll yell it...

EYE! XD
Member Since: 4 septembre 2007 Posts: 7 Comments: 8698
Quoting Detrina:
anything to be concerned about with that mess in the BoC?


Only if you're there. Looks like a cold front is responsible.

$$
GMZ082-290330-
SW GULF S OF 25N W OF 90W
430 PM CDT THU OCT 28 2010

...GALE WARNING S OF 22N W OF 95W...

.TONIGHT....W OF FRONT NW TO N WINDS 20 TO 30 KT. SEAS BUILDING
8 TO 12 FT. E OF FRONT NE WINDS 10 TO 15 KT. SEAS 2 TO 4 FT.
SCATTERED SHOWERS AND TSTMS ALONG FRONT.
.FRI AND FRI NIGHT...S OF 22
N W OF 95W NW TO N WINDS 25 TO 35 KT
DIMINISHING 25 TO 30 KT LATE FRI NIGHT. SEAS 10 TO 13 FT.
ELSEWHERE W OF FRONT N TO NE WINDS 20 TO 30 KT. SEAS 8 TO 12 FT.
E OF FRONT NE WINDS 10 TO 15 KT. SEAS 4 TO 6 FT. SCATTERED
SHOWERS AND TSTMS S OF 22N.
Member Since: Posts: Comments:
Quoting doorman79:


I have pirogues for sale cheap! ;)

Cant beat a Pirogue..
Love them.
Member Since: 24 octobre 2005 Posts: 0 Comments: 24314
SAB have 92L a T2.0. I think we'll be seeing 20L/Shary tonight.
Member Since: 2 septembre 2009 Posts: 130 Comments: 21193
Shary may be coming real soon.But of course thats the NHC call not ours.And all the system by south america needs is a closed circulation,and we'll have ourselfs a tropical depression/storm.
Member Since: Posts: Comments:
Quoting CybrTeddy:


???

This is a sub-tropical system.. not a fully tropical cyclone. Hence forth the dry air surrounding it. 92L's defiantly about to become Shary in my opinion.



Post #570 :)
Member Since: 6 juillet 2010 Posts: 113 Comments: 32072
92L


Hello. Anybody home?!
Member Since: 11 juillet 2006 Posts: 14 Comments: 11328
Quoting TropicalAnalystwx13:
90L is falling apart, and 92L is being overtaken by Shear and Dry Air.

91L is by far the most likely to become a named storm. The system already has 35 mph winds, and it is strengthened, and not at a slow pace. I'd place my bets on a Tropical Storm tomorrow...5PM or earlier.

This system has the potential to become something dangerous, with little Shear, and a favorable environment. I could see this becoming our seasons 11th hurricane.


EDITED for post 570.
Member Since: Posts: Comments:
Quoting Chicklit:
Oh yeah, guess what, Potts.
Your weekend picnic may be held inside or under cover.

...LOQ PRESSURE SYSTEM IS LOCATED ABOUT 1200 MILES NORTHWEST OF THE NORTHERNMOST CAPE VERDE ISLANDS. ALTHOUGH SHOWER AND THUNDERSTORM ACTIVITY ASSOCIATED WITH THE LOW HAS INCREASED DURING THE PAST FEW OURS...UPPER-LEVEL WINDS ARE EXPECTED TO BECOME LESS FAVORABLE FOR DEVELOPMENT ON FRIDAY. THERE IS A MEDIUM CHANCE...30 PERCENT...OF THIS SYSTEM BECOMING A TROPICAL CYCLONE DURING THE NEXT 48 HOURS AS IT MOVES SLOWLY WESTWARD.


Maybe cancelled.
60 people to move by boat to Monos Island, to party on Saturday.
The Gulf of Paria is pretty benign, most times.
But SouthWesterlies and Westerlies turn it into a Bad place to be, in a small boat.
The jetties and piers on the islands off the NW peninsula are not built to be landed on in rough conditions, and ALL the marinas are west-facing...
Member Since: 24 octobre 2005 Posts: 0 Comments: 24314
572. JLPR2
STS Shary soon...

28/2345 UTC 26.7N 62.6W T2.0/2.0 92L -- Atlantic

91L is getting there but not yet...

28/2345 UTC 8.0N 51.9W T1.5/1.5 91L
Member Since: 4 septembre 2007 Posts: 7 Comments: 8698
Quoting TropicalAnalystwx13:
90L is falling apart, and 92L is being overtaken by Shear and Dry Air.

91L is by far the most likely to become a named storm. The system already has 35 mph winds, and it is strengthened, and not at a slow pace. I'd place my bets on a Tropical Storm tomorrow...5PM or earlier.

This system has the potential to become something dangerous, with little Shear, and a favorable environment. I could see this becoming our seasons 11th hurricane.


92L is on the verge of becoming Sub-Tropical Storm Shary

Note saw your post 570, now I stand corrected lol
Member Since: Posts: Comments:
I stand corrected...

92L: 35 knots | 1006 mb | 26.8N / 62.7W

92L: Shary

91L: Tomas

90L: Nothing

That's my true, honest, opinion :D (I am cheating :P)
Member Since: 6 juillet 2010 Posts: 113 Comments: 32072
Member Since: 11 juillet 2006 Posts: 14 Comments: 11328
90L is falling apart, and 92L is being overtaken by Shear and Dry Air.

91L is by far the most likely to become a named storm. The system already has 35 mph winds, and it is strengthened, and not at a slow pace. I'd place my bets on a Tropical Storm tomorrow...5PM or earlier.

This system has the potential to become something dangerous, with little Shear, and a favorable environment. I could see this becoming our seasons 11th hurricane.
Member Since: 6 juillet 2010 Posts: 113 Comments: 32072
92L will go directly to STS Shary if named.
Member Since: Posts: Comments:
Quoting pottery:
Local weather forecasters are not impressed (Trinidad)
Rain chances-
Fri 30%
Sat 40%
Sun 30%
Mon 40%

They must be looking at a different map, to me!


I have pirogues for sale cheap! ;)
Member Since: Posts: Comments:
Quoting JLPR2:


ha! Just a itty bitty more for STS Shary then.


that qualifies it as a STS already, NHC just needs to decide whether the system as a whole is organized enough
Member Since: Posts: Comments:
564. Skyepony (Mod)
Wow~ Those two THEMIS satillites (studing northern lights) we thought were dead cause they'd settled into an orbit with not enough sun for them a few years ago... NASA moved them.. to orbit the moon.
Member Since: Posts: Comments:
Quoting Hurricanes101:


I say sub-tropical storm Shary in 6-12 hours


or 6-12 minutes LOL
Member Since: Posts: Comments:
Oh yeah, guess what, Potts.
Your weekend picnic may be held inside or under cover.

2. A VIGOROUS TROPICAL WAVE LOCATED OVER THE TROPICAL ATLANTIC ABOUT 725 MILES EAST-SOUTHEAST OF THE WINDWARD ISLANDS IS PRODUCING A LARGE AREA OF SHOWERS AND THUNDERSTORMS. THIS SYSTEM CONTINUES TO SHOW SIGNS OF ORGANIZATION...AND ENVIRONMENTAL CONDITIONS APPEAR TO BE FAVORABLE FOR GRADUAL DEVELOPMENT OF THIS DISTURBANCE DURING THE NEXT COUPLE OF DAYS.

THERE IS A MEDIUM CHANCE...50 PERCENT...OF THIS SYSTEM BECOMING A TROPICAL CYCLONE DURING THE NEXT 48 HOURS AS IT MOVES WESTWARD OR 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...VENEZUELA...AND NORTHERN PORTIONS OF GUYANA DURING THE NEXT COUPLE OF DAYS.

Member Since: 11 juillet 2006 Posts: 14 Comments: 11328
561. JLPR2
Quoting Hurricanes101:


maybe this will convince him

AL, 92, 2010102900, , BEST, 0, 268N, 627W, 35, 1006, LO


ha! Just a itty bitty more for STS Shary then.
Member Since: 4 septembre 2007 Posts: 7 Comments: 8698
Current ATCF summary:

90L: 30 knots | 1011 mb | 25.6N / 41.8W

90L pressure continues to rise...

92L: 35 knots | 1006 mb | 26.8N / 62.7W

92L pressure has dropped 3mb since the last update, and winds have increased to TS strength...
Member Since: Posts: Comments:
559. JLPR2
Quoting MiamiHurricanes09:
That's the exact same buoy I'm looking at. 41049.


Yep that buoy will give us a better idea of how 92L is doing tonight.
Member Since: 4 septembre 2007 Posts: 7 Comments: 8698
Quoting Skyepony:


This has most of them & some what brief.


Thank you.

It looks like alot of rain in the future in the caribbean.

Here in Jamaica we have several communities that are becoming submerged become of rising water. One community called "Chigwell" was featured last night. Unbelievable... a lake where a community use to be...
Member Since: 17 août 2008 Posts: 0 Comments: 672
Quoting MiamiHurricanes09:
I agree. Buoys in the area are reporting gale force winds displaced well from the center further reinforcing that this system is subtropical in nature.


maybe this will convince him

AL, 92, 2010102900, , BEST, 0, 268N, 627W, 35, 1006, LO
Member Since: Posts: Comments:
anything to be concerned about with that mess in the BoC?
Member Since: Posts: Comments:
ATCF shows that 92L's pressure has decreased 3mb to 1006mb and winds have increased to 40mph. Subtropical Storm Shary looks imminent.

AL, 92, 2010102900, , BEST, 0, 268N, 627W, 35, 1006, LO,
Member Since: 2 septembre 2009 Posts: 130 Comments: 21193
Quoting Hurricanes101:


yes it is
And out of all the times someone said" this should have been classified as a depression already" This system definitely looks like a tropical depression..
Member Since: Posts: Comments:
Local weather forecasters are not impressed (Trinidad)
Rain chances-
Fri 30%
Sat 40%
Sun 30%
Mon 40%

They must be looking at a different map, to me!
Member Since: 24 octobre 2005 Posts: 0 Comments: 24314
"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."

-- Senior NHC Hurricane Specialist Dan Brown

Cool beans.
Dr. Jeff Masters reporting from inside the hive.
Member Since: 11 juillet 2006 Posts: 14 Comments: 11328
Quoting JLPR2:
Pressure at a buoy very close to 92L is dropping like a rock with the winds picking up slightly, strongest winds are probably far away from the center.

That's the exact same buoy I'm looking at. 41049.
Member Since: 2 septembre 2009 Posts: 130 Comments: 21193
Quoting Hurricanes101:
yup 92L is a subtropical feature and because of that, the convection does not have to be right over the center

I think 92L has a very good chance of being Sub-tropical Storm Shary
I agree. Buoys in the area are reporting gale force winds displaced well from the center further reinforcing that this system is subtropical in nature.
Member Since: 2 septembre 2009 Posts: 130 Comments: 21193
Quoting JLPR2:
Pressure at a buoy very close to 92L is dropping like a rock with the winds picking up slightly, strongest winds are probably far away from the center.



I say sub-tropical storm Shary in 6-12 hours
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547. JLPR2
Pressure at a buoy very close to 92L is dropping like a rock with the winds picking up slightly, strongest winds are probably far away from the center.

Member Since: 4 septembre 2007 Posts: 7 Comments: 8698
Quoting JLPR2:


Yep, very pretty on visible.


But is the anticlone currently on top of it supposed to follow it into the Caribbean?

THIS One is one to worry about and it should probably be a TD already.. yes the anti cyclone over it belongs to it and unless sheared away in the next 48 hours is forecast to follow it in the upper air GFS charts
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545. JLPR2
Quoting Hurricanes101:


yes it is


Ah, well, I was kinda hoping you wouldn't say yes. XD
Member Since: 4 septembre 2007 Posts: 7 Comments: 8698
yup 92L is a subtropical feature and because of that, the convection does not have to be right over the center

I think 92L has a very good chance of being Sub-tropical Storm Shary
Member Since: Posts: Comments:
543. Skyepony (Mod)
Quoting kimoskee:
Good evening.

Can anyone recommend a link that gives a good tutorial (for us non-mets) on the various models.

Thanks.


This has most of them & some what brief.
Member Since: Posts: Comments:
Quoting JLPR2:


Yep, very pretty on visible.


But is the anticlone currently on top of it supposed to follow it into the Caribbean?


I personally haven't looked but, word on the street is yes.

91L looks like a mid-September "Big Dog"
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This 91L keeps growing..Look at all that water this system covers..
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540. JLPR2
Quoting sailingallover:

Because it is?
I think they are just lettting the DOC play!!
The sat loops are really from July.. no wait the dust is missing..replaced by dry air..cool tools they got there at NHC..
Ok looking at 92 and all the dry air around it and shear and water temps I think 70% is nuts..
it's close to 26 deg water and the ULL is pounding it flat...center is almost exposed..


As you can tell by the smiley at the end of the question I wasn't actually asking it seriously.
And 92L's % is perfectly fine since the NHC is probably thinking subtropical, the NHC knows what it is doing.
Member Since: 4 septembre 2007 Posts: 7 Comments: 8698
Quoting JLPR2:


Yep, very pretty on visible.


But is the anticlone currently on top of it supposed to follow it into the Caribbean?


yes it is
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Quoting JLPR2:
So we got three disturbances with 70%, 50% and 30% of development out int eh ATL on October 28...

Now why does that sound weird? XD

Because it is?
I think they are just lettting the DOC play!!
The sat loops are really from July.. no wait the dust is missing..replaced by dry air..cool tools they got there at NHC..
Ok looking at 92 and all the dry air around it and shear and water temps I think 70% is nuts..
it's close to 26 deg water and the ULL is pounding it flat...center is almost exposed..
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537. JLPR2
Quoting CyclonicVoyage:


Best looking invest I've seen in a while. Textbook pre-TD structure, big too.


Yep, very pretty on visible.


But is the anticlone currently on top of it supposed to follow it into the Caribbean?
Member Since: 4 septembre 2007 Posts: 7 Comments: 8698
Good evening.

Can anyone recommend a link that gives a good tutorial (for us non-mets) on the various models.

Thanks.
Member Since: 17 août 2008 Posts: 0 Comments: 672
I must say, 500 post late, but GREAT post Dr. M!
Member Since: Posts: Comments:
Quoting CyclonicVoyage:


Best looking invest I've seen in a while. Textbook pre-TD structure, big too.


Agreed and conditions are favorable for development, plenty of moisture and shear is favorable
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533. Skyepony (Mod)
91L Average Position Error (nm) for core models
model Error Trend 24hr Error 48hr Error 72hr Error Day 4 Error Day 5 Error
HWRF DECREASING 74.2 -1 -1 -1 -1
LBAR DECREASING 95.7 -1 -1 -1 -1
BAMD DECREASING 119 -1 -1 -1 -1
MM5E DECREASING 132.2 -1 -1 -1 -1
MM5B DECREASING 147.6 -1 -1 -1 -1
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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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