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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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
Member Since: Posts: Comments:
Quoting sailingallover:

Lots of shear...and although the wave itself is moist there is a lot of dry air around too..



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

while 92 has a high probability of forming according to NHC it's convection is weak and almost sheared off by the ULL to it's SE the front/trough is going to eat it in 48 hours or less.. it will not have time to make a large trough down into the Caribbean.
You are talking in a funny way this evening.
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530. JLPR2
Quoting HurricaneDean07:
what i find wierd is that all the percentages' first #'s are odd. 70,50,30.


ha! XD Hadn't noticed that one.
Member Since: September 4, 2007 Posts: 7 Comments: 8690
Quoting sailingallover:

Lots of shear...and although the wave itself is moist there is a lot of dry air around too..



There is a huge anti-cyclone over it

I really do not know what you are looking at for any of these systems
Member Since: March 10, 2010 Posts: 1 Comments: 7683
Quoting hydrus:
The models have been trending westward...


You mean landward??

JK

That would explain the lack of population.
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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
what i find wierd is that all the percentages' first #'s are odd. 70,50,30.
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Quoting CyclonicVoyage:
Still not a lot of takers on 91L.


Lots of shear...and although the wave itself is moist there is a lot of dry air around too..

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Quoting CyclonicVoyage:
Still not a lot of takers on 91L.

The models have been trending westward...
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523. JLPR2
So we got three disturbances with 70%, 50% and 30% of development out in the ATL on October 28...

Now why does that sound weird? XD
Member Since: September 4, 2007 Posts: 7 Comments: 8690
Quoting 2ifbyC:


When I was stationed in Denver back in the '70s, a local radio station ran a local contest.

First prize... a weekend in Leadville

Second prize... a week in Leadville
I hate to think what third woulda been if ther wuz wun....;0
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Quoting Neapolitan:

You did mean 90L, correct?

while 92 has a high probability of forming according to NHC it's convection is weak and almost sheared off by the ULL to it's SE the front/trough is going to eat it in 48 hours or less.. it will not have time to make a large trough down into the Caribbean.
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Quoting sailingallover:

no 92 the one north of the VI's
LOL. never thought that i would say this in late Ocotber but there is so many invests that people are getting confused which one other people are talking about.
XD
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Quoting sailingallover:

no 92 the one north of the VI's
Why are you being silly this evening? Have you been out this evening at the pub?
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Quoting Neapolitan:
Leadville is at 10,152 feet in the Rockies, but still...)


When I was stationed in Denver back in the '70s, a local radio station ran a contest.

First prize... a weekend in Leadville

Second prize... a week in Leadville
Member Since: Posts: Comments:
Quoting CyclonicVoyage:


Dr. Masters is there to help.
its a good thing too. the NHC people would be tearing their hair out without him to help. Theres going to be a pretty big blog on what happend tonight at the NHC
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Quoting sailingallover:

no 92 the one north of the VI's


At 70% now, NHC indicates both the circulation and the convection are better organized
Member Since: March 10, 2010 Posts: 1 Comments: 7683
Quoting Neapolitan:

You did mean 90L, correct?

no 92 the one north of the VI's
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Quoting HurricaneDean07:
Looks like all the invest want to form at the same time. gonna have some trouble at NHC trying to name all these at once.


Dr. Masters is there to help.
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Still not a lot of takers on 91L.

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Looks like all the invest want to form at the same time. gonna have some trouble at NHC trying to name all these at once.
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Quoting washingtonian115:
Looks as though he's already in a bad mood.I wouldn't want to start with him.Lets keep it drama free tonight.Besides we have better things to talk about more than what he said in his post.


No argument there. Any drama won't be perpetuated here. A serious situation could be in the offing.
Member Since: July 23, 2010 Posts: 1 Comments: 12414
Quoting winter123:
blog is dead for 1 almost TD and 2 almost STDs!


Std's? please don't remind me of my younger days lol!
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South indian season just started -
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Quoting Hurricanes101:


Someone took away his favorite blankie
Looks as though he's already in a bad mood.I wouldn't want to start with him.Lets keep it drama free tonight.Besides we have better things to talk about more than what he said in his post.
Member Since: August 14, 2010 Posts: 10 Comments: 16971
Quoting hydrus:
Ivan may have formed down around 8 degree,s.

Ivan formed around 8deg and then went up to 13 then back down...but was a hurricane at 10N.
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Quoting hydrus:
And if that high pressure area moves right along with 91L, this will almost certainly become a major hurricane..


Agreed. Something to be reckoned with.
Member Since: July 23, 2010 Posts: 1 Comments: 12414
blog is dead for 1 almost TD and 2 almost STDs!
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Quoting kmanhurricaneman:
Link ivan 2004
lol..Oh well..It did get down to 8.9..:)
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Quoting KerryInNOLA:
Quoting KEEPEROFTHEGATE:
sorry to all members for my little outburst but NHC bashing is something i will not stand for they deserve more than just our respect
Yes Keeper.They deserve it. They are true Americans worthy of a Hollywood movie. I sometimes dream about the NHC and I bet you do too.


You liked the guy pointing at the screen huh!
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Quoting sailingallover:
Now that 92 looks to be not developing there is less of a chance of 91 getting pulled north over PR and the VI's.

You did mean 90L, correct?
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Quoting Hurricanes101:


Someone took away his favorite blankie


Nice!!
Member Since: July 23, 2010 Posts: 1 Comments: 12414
Quoting PSLFLCaneVet:


That doesn't bode well. KOTG's bad feeling may come to pass.
And if that high pressure area moves right along with 91L, this will almost certainly become a major hurricane..
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Link ivan 2004
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Evening all.

91L's got that August / September pre-TD look to it this evening.

She/He is well on it's way folks, it's a big en' too.


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Quoting Grothar:
Image with shear maps overlay.



Grothar, I had a good day! now you trying to depress me!
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Quoting PSLFLCaneVet:


Wow, harsh words. Bad day for you?


Someone took away his favorite blankie
Member Since: March 10, 2010 Posts: 1 Comments: 7683
Quoting sailingallover:
91 is something to worry about..
It should go through the windwards as a rain wind event. An earlier windsat showed a large area of 35 knot winds to the north but no closed circulation as of 24 hours ago but the latest sat loops looks like it has one. Regardless heavy rain and strong squalls for the windwards.

Then what?
Now that 92 looks to be not developing there is less of a chance of 91 getting pulled north over PR and the VI's. But again Sat loops shows clouds moving NW from just north of Barbados to the center of 92L so it is dragging a bit of a trough and 91 could still go up into this as some models show. The other option is it goes more westerly as a High builds in from the NW under 92L in 60+ hours. The ECMWF has a 1021 High over the DR so throw that out.The GFS build in the high but leaves a trough. Then a Low forms in the GOM and blocks movement and it stalls south of Haiti for 4 days before moving NE
And the upper level low north of the DR now is forecast to move off to the north leaving a zonal flow and take the very strong shear with it.
The synopsis..
If 91 develops fast and moves fast it may get caught up by the trough and upper level winds from 92 and it's ULL and zip up to the VI's
Or it will not make it to the trough/ULL in time and cross to just under haiti where it may stall and wash us all away as it wanders in a circle..


The chances of 92L just went up to 70% and there is a good chance it will develop, so not sure where you are getting that it appears 92L is not developing
Member Since: March 10, 2010 Posts: 1 Comments: 7683
Quoting AstroHurricane001:
91L is a huge tropical system. Some potential of threatening Hispanola as a significant hurricane.


and the us
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Quoting acyddrop:


I wish people would stop wasting my bandwidth personally linking HWRF and GFDL model graphics without an actual storm and some days of hard data.


Wow, harsh words. Bad day for you?
Member Since: July 23, 2010 Posts: 1 Comments: 12414
91 is something to worry about..
It should go through the windwards as a rain wind event. An earlier windsat showed a large area of 35 knot winds to the north but no closed circulation as of 24 hours ago but the latest sat loops looks like it has one. Regardless heavy rain and strong squalls for the windwards.

Then what?
Now that 92 looks to be not developing there is less of a chance of 91 getting pulled north over PR and the VI's. But again Sat loops shows clouds moving NW from just north of Barbados to the center of 92L so it is dragging a bit of a trough and 91 could still go up into this as some models show. The other option is it goes more westerly as a High builds in from the NW under 92L in 60 hours. The ECMWF has a 1021 High over the DR so throw that out.The GFS build in the high but leaves a trough. Then a Low forms in the GOM and blocks movement and it stalls south of Haiti for 4 days before moving NE
And the upper level low north of the DR now is forecast to move off to the north leaving a zonal flow and take the very strong shear with it.
The synopsis..
If 91 develops fast and moves fast it may get caught up by the trough and upper level winds from 92 and it's ULL and zip up to the VI's
Or it will not make it to the trough/ULL in time and cross to just under haiti where it may stall and wash us all away as it wanders in a circle..
Hopefully something will change...
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Quoting acyddrop:


I wish people would stop wasting my bandwidth personally linking HWRF and GFDL model graphics without an actual storm and some days of hard data.


oh you poor thing, you make it like you are the only one of this blog lol

Does your bandwidth need a band-aid or something?
Member Since: March 10, 2010 Posts: 1 Comments: 7683
Quoting bajelayman2:
When was the last time anything cropped up from this low, anyone remember??? I cannot, Ivan came from acroos, around 10N I think, but did not start as low as this one.....as for before that, I cannot remember any starting this low downm before it reached us in barbados.
Ivan may have formed down around 8 degree,s.
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Evening all!

Wow,

Who pi$$ed in ma natures cornflakes this morning! Pottery if ya need a rain coat, Fed ex may have it in time if I send it now!
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Quoting Grothar:
Image with shear maps overlay.



That doesn't bode well. KOTG's bad feeling may come to pass.
Member Since: July 23, 2010 Posts: 1 Comments: 12414
Quoting kmanislander:


Just more hype from the HWRF. It showed the same for Richard all the way to Fla. LOL


I wish people would stop wasting my bandwidth personally linking HWRF and GFDL model graphics without an actual storm and some days of hard data.
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Quoting Grothar:
Image with shear maps overlay.

It has the almighty anticyclone on top of it.Something that the stronger storms earlier this season had....not good.And why you switch your avatar?
Member Since: August 14, 2010 Posts: 10 Comments: 16971

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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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