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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Quoting pottery:

Whew!
Good to "meet" you.


I bow to your magnetic personality.
Member Since: Posts: Comments:
Link
Member Since: September 27, 2007 Posts: 1 Comments: 21060
Quoting KerryInNOLA:
Relax.Any day it will be November. Really bad storms don't form in November.

Maybe you did'nt notice, but Climo is out the window, right now...
Member Since: October 24, 2005 Posts: 0 Comments: 24265
Quoting 1900hurricane:
91L reminds me of the season's first 92L on steroids! That thing is huge.
I was just thinking that...
Probably will have the same effect for us too..
Member Since: September 1, 2009 Posts: 23 Comments: 1007
Quoting Grenada:


It is certainly depressing me.


I have to agree, this system is almost classic in appearance - maybe that's the catch, looks can be deceiving ... time will tell eventually - but still its commanding a hugh area (700 miles) of the atmosphere in the surroundings and its does have rotation, no question there.

Not to mention all that really WARM SST's I've on about for the last few weeks in that area of the Tropical Atlantic. Wind Shear seems low enough not to be a serious issue, and forecasted steering curents seem likely to push it more northwestward and in the general direction of the Windward Islands.
Member Since: June 3, 2002 Posts: 0 Comments: 64






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Quoting DDR:

I know where your coming from,i got lots a family in Grenada,heard all the stories they told,not nice at all.

I am not surprised to see the models trending a little more north right now.
As the system gets more organised it should tend to do that.
Also, a lot of upper level flow is acting on it, pushing it away somewhat.

It's a very big one though, we will all get some weather down here from this.
How much ????
Member Since: October 24, 2005 Posts: 0 Comments: 24265
Quoting pottery:

Whew!
Good to "meet" you.



And you, I don't understand half of what you guys talk about but have been reading you all for a long time, these days I like to know what is heading our way well in advance.
Member Since: August 21, 2010 Posts: 0 Comments: 96
Quoting Chicklit:
Stealth Mode 91L


How can anything that large even dream of being stealthy??? XP
Member Since: Posts: Comments:
How soon do you think Trinis will start to panic? CNC3 news mentioned that rumours were in abundance of a trpoical storm approaching.
Member Since: August 24, 2006 Posts: 0 Comments: 52
91L looks like it will need to be watched carefully here in Jamaica. Our friends in Trinidad & Tobago and Northern part of South America will have to pay attention...
Member Since: September 12, 2010 Posts: 0 Comments: 61
Quoting pottery:

The Gulf of Paria is closed, and is not very big.
So swells are not an issue.
But the chop can get real nasty, and boats are lost every year...
My son in law lost his, a couple years ago, from a system like this one (name slips me).
I told him he was in a bad place, but he did'nt move.
Boat went down in 60', between 1:00am and daylight.
He salvaged, but lost plenty stuff.

Here we get 12'+ waves on the northside sometimes boats get destroyed if left at anchor..it does give us surfing though.
I need to visit there one day..last frontier of cruising I'll send a message sometime.
Member Since: September 1, 2009 Posts: 23 Comments: 1007



91L still
Member Since: July 11, 2006 Posts: 14 Comments: 11293
Quoting Grenada:


'She' got you :)

Whew!
Good to "meet" you.
Member Since: October 24, 2005 Posts: 0 Comments: 24265
666. DDR
Quoting Grenada:


Not sure that makes me feel better, Emily (10 months after Ivan) was Cat 1 and just as scary as Ivan if not more so because we knew what was coming....

I have family in Grenada,heard all the stories they told,not nice at all.
Member Since: Posts: Comments:
Quoting sailingallover:

I was being nice and left out sheared..
Judging from the low level cloud movement and lack of convection at a distance from the center I'd still classify it tropical..but the dry air and ULL's and now SST's are killing convection.
The OHC in that water can't be very high anymore..
I agree...Itsa fighter tho..
Member Since: September 27, 2007 Posts: 1 Comments: 21060
Quoting pottery:

Heh!
He/She is in Grenada.
Knows I meant "nice post". It's Caribbean-speak..
(I hope)


'She' got you :)
Member Since: August 21, 2010 Posts: 0 Comments: 96
Quoting hydrus:
Almost looks like this..
And we almost saw something like that this season.
Member Since: August 14, 2010 Posts: 10 Comments: 16902
Quoting hydrus:
Hang tight. You will be alright. You might get cat-1 winds though...


Not sure that makes me feel better, Emily (10 months after Ivan) was Cat 1 and just as scary as Ivan if not more so because we knew what was coming....
Member Since: August 21, 2010 Posts: 0 Comments: 96
Dear 91L,

I really need a vacation or people may get hurt. I am going to Bonaire in 2 weeks and I want an amazing trip. Please don't damage anything and take your trash with you. Thank you.


Largeeyes
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660. DDR
Quoting Grenada:


I took a couple of years ago, it was in a mandarin tree, only a baby.

cool
there are some large ones around here
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Quoting doorman79:


How Rude! ;P

Heh!
He/She is in Grenada.
Knows I meant "nice post". It's Caribbean-speak..
(I hope)
Member Since: October 24, 2005 Posts: 0 Comments: 24265
658. DDR
Pottery if i told you i wasn't worry by the looks of 91L i'd be lieing.
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Quoting DDR:

Nice photo Grenada


I took a couple of years ago, it was in a mandarin tree, only a baby.
Member Since: August 21, 2010 Posts: 0 Comments: 96
looks like rare occurrence of anticyclone lining up with center of circulation.
relieved to hear potts' island adventure will be postponed.
Member Since: July 11, 2006 Posts: 14 Comments: 11293
91L reminds me of the season's first 92L on steroids! That thing is huge.
Member Since: Posts: Comments:
Quoting hydrus:
Now youve done it.......YOU hurt 92,s feelings, now it will strengthen and probably hit Bermudi....

I was being nice and left out sheared..
Judging from the low level cloud movement and lack of convection at a distance from the center I'd still classify it tropical..but the dry air and ULL's and now SST's are killing convection.
The OHC in that water can't be very high anymore..
Member Since: September 1, 2009 Posts: 23 Comments: 1007
Quoting CybrTeddy:


Thankyou for posting that graphic.I see the conversation of 92L not being a sub tropical system has almost ceased.
Quoting reedzone:
Is it really late October?? Seems like late September.

Good god of mighty.Look at 91L.It's huge.But the thing is with these large cyclones they may take sometime to get going.
Member Since: August 14, 2010 Posts: 10 Comments: 16902
Quoting reedzone:
Is it really late October?? Seems like late September.

Almost looks like this..
Member Since: September 27, 2007 Posts: 1 Comments: 21060
Quoting Chicklit:

great pic reed


Yeah, I like the rainbow imagery. 91L looks to be gaining TD status tomorrow. When I see scattered convection swirl around an invest, the next day, a blow up of deep convection forms and the invest is classified. We'll see what happens. I think 92L will be classified by the morning, making 91L Thomas afterwards, just my 2 cents :)
Member Since: July 1, 2008 Posts: 13 Comments: 7365
Quoting Grenada:


It is certainly depressing me.
Hang tight. You will be alright. You might get cat-1 winds though...
Member Since: September 27, 2007 Posts: 1 Comments: 21060
649. DDR
Quoting Grenada:


It is certainly depressing me.

Nice photo Grenada
welcome islander
Member Since: Posts: Comments:


91L
Member Since: July 11, 2006 Posts: 14 Comments: 11293
Statistical/Simple Models


Dynamic Models


Early Model Wind Forecasts


Link
Member Since: Posts: Comments:
Quoting pottery:

Nice!


How Rude! ;P
Member Since: Posts: Comments:
Quoting Chicklit:
Stealth Mode 91L


Lovely image!
Member Since: October 24, 2005 Posts: 0 Comments: 24265
Unfortunately the anticyclone is continuing to stay contact with 91L, moving WNW with it, I don't think shear is going to hammer it much any more. This could be a dangerous situation setting up for the Islands.
Member Since: July 1, 2008 Posts: 13 Comments: 7365
Stealth Mode 91L

Member Since: July 11, 2006 Posts: 14 Comments: 11293
Quoting Grenada:


It is certainly depressing me.

Nice!
Member Since: October 24, 2005 Posts: 0 Comments: 24265
Seems the size of 91L will do wonders for the dry air around. Long way from the outer edge to the center.
Member Since: Posts: Comments:
good night all lets see what 91L will do tonight
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637. JLPR2
Quoting JRRP:


hey hey ...


Models trending further north, well... I wouldn't mind a storm on Monday my brain hurts from the three exams from this week and I got two more next week so yeah... bring it on! XD
Member Since: September 4, 2007 Posts: 7 Comments: 8669
Quoting hydrus:
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..


It is certainly depressing me.
Member Since: August 21, 2010 Posts: 0 Comments: 96
Quoting sailingallover:

We have that problem here.. because of the trades most anchorages,docks etc are open to the SW.. so when storms go by and the winds come from there we lose boats and when you add in the north swell from storms there is almost no where to put your boat..

The Gulf of Paria is closed, and is not very big.
So swells are not an issue.
But the chop can get real nasty, and boats are lost every year...
My son in law lost his, a couple years ago, from a system like this one (name slips me).
I told him he was in a bad place, but he did'nt move.
Boat went down in 60', between 1:00am and daylight.
He salvaged, but lost plenty stuff.
Member Since: October 24, 2005 Posts: 0 Comments: 24265
Quoting Chicklit:


..maybe they just have the satellite positioned in the wrong place, oops.
Doc is probably fiddling with the knobs again...when I saw that loop of andrea I though wow I am looking in the wrong place!! then I saw the date..
Member Since: September 1, 2009 Posts: 23 Comments: 1007

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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.