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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This looks like TD or weak TS to me not a 30% invest.
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POSS T.C.F.A.
INV/91L/XX
MARK
8.58n/50.28w
Member Since: July 15, 2006 Posts: 173 Comments: 54283
Happy now Amy. Mind you that picture was taken a few years ago. And no wise cracks, hydrus!
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91L looks like yet another invest that should be in the West Pacific, we've had so many large "West-Pacific" looking systems this year, I'd be interested to figure out what's causing this anomaly.
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Quoting kmanislander:


Maybe a pic of a Viking ??


How is that, I just changed it. LOL
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Quoting kmanislander:


Just more hype from the HWRF. It showed the same for Richard all the way to Fla. LOL
lets hope it is just hype but i got to tell yeah i believe 91 l will be scary shary for a halloween nightmare but iam hoping not
Member Since: July 15, 2006 Posts: 173 Comments: 54283
Quoting Grothar:
Doesn't look good.

Looks ok
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Quoting KEEPEROFTHEGATE:
if ya want to see sumin scary wellhere ya go


Just more hype from the HWRF. It showed the same for Richard all the way to Fla. LOL
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Quoting KEEPEROFTHEGATE:
if ya want to see sumin scary wellhere ya go


And it's not even Halloween. Not good Keeper, they don't need something like that! Yes, very scary. Never thought I would lived to see a storm that late in October, but then again, if you live over 500 years, you're bound to see a lot. OK, hydrus have fun.
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Quoting Grothar:


That is a Viking Ship that my ancestors sailed on to settle Greenland when it was tropical. LOL. Would you rather I upload a picture of myself so you can all have a good laugh???


Maybe a pic of a Viking ??
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Quoting Grothar:
Doesn't look good.

This system has increased its banding features and the outflow is looking better by the minute..I would be surprised if the NHC did not up 91L to T.D. status at the 11 P.M. advisory.
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Quoting NRAamy:
Grothar.... I like the old avatar better... this one needs a tan....

;)


That is a Viking Ship that my ancestors sailed on to settle Greenland when it was tropical. LOL. Would you rather I upload a picture of myself so you can all have a good laugh???
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91L showing a much improved vorticity signature but more importantly the feature is now much farther North and closing in on 10 degrees. It is obviously now on a WNW heading which should allow the low center to just skim the North coast of SA and make its way into the Caribbean.

Trinidad and Tobago look to have some heavy weather on the way.

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Quoting hydrus:
Not even remotely.

Nope, not one bit.

Link
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Quoting Grothar:
Doesn't look good.

if ya want to see sumin scary wellhere ya go
Member Since: July 15, 2006 Posts: 173 Comments: 54283
Quoting 1900hurricane:
Hmm, there apparently is a gunman on my campus armed with an AK47. Not cool...
Not even remotely.
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Link
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Doesn't look good.

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Grothar.... I like the old avatar better... this one needs a tan....

;)
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Good news. The steering layer map from CIMSS is back up for the Caribbean just in time for 91L

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Hmm, there apparently is a gunman on my campus armed with an AK47. Not cool...
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We could see Shary soon.
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Quoting TropicalAnalystwx13:


So does that mean it was stronger than 90 mph? Like maybe 95 mph, or even 100 mph???
The 92 mph winds were about in the center of the storm people were saying it had been quiet for 1/2 an hr so i think the northern eye wall could have been close to 100
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Dr M,
Enjoyed reading your story. Neat peek inside the NHC. Thanks.

(mod)
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Quoting KEEPEROFTHEGATE:


our 91L looks to be heading just ne of trinny
91L looks to be even further south then 1963,s Flora..
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Intense convection with 92L:





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our 91L looks to be heading just ne of trinny
Member Since: July 15, 2006 Posts: 173 Comments: 54283
Quoting belizeit:
Good Day here is some information on Richard .
Richard had 92 mph winds 50miles inland


So does that mean it was stronger than 90 mph? Like maybe 95 mph, or even 100 mph???
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Outflow seems better the past few hours..Appears to be fanning out in the upper levels..
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...NOT A REAL TROPICAL WEATHER OUTLOOK ISSUED BY THE NATIONAL HURRICANE CENTER...



TROPICAL WEATHER OUTLOOK
530 PM EDT THU OCT 28 2010
TROPICALANALYSTWX13 - WUNDERGROUND.COM

90L: Showers and thunderstorms associated with an area of low pressure located about 1200 miles to the NE of the Cape-Verde Islands remains very disorganized. Even though winds are high enough for the system to be classified, the system lacks the structure. The environment is becoming increasingly unfavorable, and further develop is possible, but not entirely likely. There is a Medium Chance...30%...of this system becoming a Tropical Cyclone in the next 48 hours.

91L: Showers and thunderstorms associated with a vigorous disturbance located about 825 miles to the SSE of the Windward Islands appears to be strengthening fairly quickly. The structure of this system is significantly better compared to 90L, and therefore, the system has a higher chance. There is a Medium/High Chance...50% to 60%...of this system becoming a Tropical Cyclone within the next 48 hours.

92L: A tropical wave located to the SE of Bermuda is producing organized showers and thunderstorms. The structure of this system is that of 91L's, which is really good. The environment is currently favorable for further development, but is expected to become less favorable over the weekend. This system has a high likelihood of developing, but it should not affect the USA directly. There is a High Chance...70%...of this system becoming a Tropical Cyclone within the next 48 hours.

~ TropicalAnalystwx13
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91L is stealing the show on satellite.
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Quoting KEEPEROFTHEGATE:
XX/XX/AOI

That will likley not develope.

actually there will be a dev. gale area there

Member Since: July 15, 2006 Posts: 173 Comments: 54283
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Quoting belizeit:
Good Day here is some information on Richard .
Richard had 92 mph winds 50miles inland

I'm not surprised, Richard had a very good structure when going inland. In fact, if it weren't for the landfall, I think he was on the verge of bombing out:

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Good Day here is some information on Richard .
Richard had 92 mph winds 50miles inland
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294. unf97
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


I agree. For the most part, I think the forecasters at NHC have done a very good job overall with their analysis of this busy storm season. I respect greatly what they do and the difficulties of what comes with their jobs down there on a daily basis.

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Quoting KEEPEROFTHEGATE:
XX/XX/AOI
That will likley not develope.
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
I've already tooken care of the problem KOTG.
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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
Very true.Very good hearted people. It is sad that someone would post a comment like that.
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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
Member Since: July 15, 2006 Posts: 173 Comments: 54283
Quoting gordydunnot:
I must say, the end of the season sure looks like a barn burner.Have to commend the hyper caster's.
this season is definitely going out in a bang, if all these invests eventually form we would be dealing with our next storm being WALTER!! this is one hyper active season. if this does happen i wouldnt be surprised if we see the greek alphabet
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Looks like 90L is becoming a multi vortex storm, maybe another invest 99L/Richard? as in it have multi vortexes that wrap around one large circulation before forming.
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Quoting sunlinepr:
we have been so focused on if 90L or 92L Would be named shary that now 91L wants to get in on the fight for the name.
Very Organized Tropical Wave!!
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I must say, the end of the season sure looks like a barn burner.Have to commend the hyper caster's.
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thanks
Member Since: July 15, 2006 Posts: 173 Comments: 54283
< Already done.
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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.