My report on Arlene

[Matt-hurricanewatcher]

Unoffical discussion...This is not offical it is just my thinking...

The following post is NOT an official forecast and should not be used as such. It is just the opinion of the poster and may or may not be backed by sound meteorological data. It is NOT endorsed by any professional institution including storm2k.org For Official Information please refer to the NHC and NWS products.

Tropical storm Arlene
Report one
Forecaster Matthew
6-11-2005


Arlene was a Western Caribbean tropical storm that moved into the Gulf of Mexico. Finally making landfall on the 11th of June, near PENSACOLA FLORIDA around 2:20pm cdt.


System discussion


A area of convection started to form over the Eastern Pacific, off the coast of central America. Late on the 6th into early on the 7th of June. This area moved slowly to the north over the next 24 hours. Developing into a area of low pressure over Honduras. Shear upwards of 40 knots where covering the western Caribbean. But a strong upper level high was stronging to form. So once this system moved into the western Caribbean the upper level winds where between 15 to 20 knots...Or 10 to 15 knots of decrease over the past 24 hours. Over night that area of low pressure moved out into the western Caribbean. In by early on the 8th was developing.

I'm thinking that it was oreganized around 2pm est to become a depression. But recon did not get into the system intill 5pm est for the upgrade. The system was very poorly defined...With recon finding a non warm core later that night. Also with the fact that the wind field was so broad. We are thinking that durning the first 12 hours of this system it was subtropical. Also the recon reports where coming an with 20 to 25 knot flight level winds. So any winds of 25 mph or more where with in the bands to the northeast quad. The system stayed disoreganized for days dealing with some shear/dry air. Durning the day on the 9th the convection formed to the east of a exposed LLC. So all the real winds where reported there.

But at the same time the LLC was getting stronger from the 1004 milibars pressure to 1002 milibars. But the winds remained far from of the center. As the system moved northward...A side note is buoy's where showing its winds slowly increasing over time. By later on the morning of the 9th(8am nhc special advvisorie) A ship 130 n mi northeast of the LLC. Found winds of 40 knots. Which caused the upgrade. The winds closer to the LLC where around 25 to 30 mph. It is a suprize that a report this far away from the LLC would carry water.

Late on the 9th into the 10th the LLC was slowly getting strong. In the recon reports showed with 45 knot reports...But the system was starting to become many centers moving with an a large/broad cirualtion. Even so this system has become even less oreganized/convection wise. The LLC(Over all LLC)Was becoming stronger. The system by early on the 10th of June had moved into the Cuba/Yact channel. In had no convection over its LLC. But it was becoming much better defined. Around 4am 10th June you could also see convection forming north of Cuba.

By 10am 10th of June. The system had reformed to the north around 84.9 west/24.0 north. Deep convection was wraping around the LLC. On the tampa radar shown that the system had gained very favable banding on the eastern quad. The recon found that this system was up to 64 knots flight level(Reported 110 nm northeast) Or 74 mph flight level. But because of the dry air, which might of kept it from reaching the surface. 55 knots or 60 mph surface winds. A buoy to the southwest of the convection shown that the center had reformed close to the convection. With the winds turning into the convection. The system had once again became disoreganize later around 2pm est. With two centers forming. But a report of 997 milibars with 69 knot winds had been found. The convection kept trying ever harder to cover the center. 69 knots=79 mph flight level. Surface around (Also dry air theory) down to 65 mph. The LLC was moving northward. But a high pressure over the Atlantic would soon force it to turn northwestward later that night.

A new stronger LLC was forming as the system turned northwestwad. The pressure was falling very fast. With reports of 997 millibars at 5pm est. 992 millibars at 8pm...In by 11pm 989 milibars. The system was becoming much better oreganized with a large area of convection forming over its northern/northeastern quad. Recon shown that winds where at flight level 75 knots=86 mph or reduced 90 percent to 75 mph or 80 percent down to 60 knots. Also because the convection was weak/dry ari mixing that the surface winds are downed to 60 knots=70 mph. Which makes this a strong tropical storm. The outflow over the northern/western quads where spreading. The system was moving west-northwestward by both the nhc recon/radar data. By 2am the 11th the system was feeling the affects of dry air. In also the system had turned more northwestward. Centered around 27.5/86.6 west. By the early morning hours the convection had almost totally faded away. But the system still had a amazing satelite/oreganizion. By 6am est the system was for the first time in its whole life moving around one LLC. Radar shown a 50 percent closed eye. The convection came back later on the 11th.

The surface reports later morning shown that this system did not have a strong wind field. With winds of 50 mph tops. Because of the dry air that got into the system. It had nearly a closed eye but weaken to 50 mph. What happens is there is not enough convection to push the winds to the surface. On landfall the system did have a closed eye...Even so not well defined. But Max winds shown was only around 45 mph. But those winds where reported a few miles inland. Because of hurricane Ivan of 2004 most of the reporting stations where distoryed. We are going with 60 mph at landfall because of this. Another update will likely need to be done.

The system then moved northward...In faded into history...

Max winds 60 knots
Min Pressure 989 millibars


Creits
Nhc
Recon flight sq
Noaa Satellite
The national buoy center.


I hope this go's over well. Tell me where I'm wrong or right. Thanks for your option.

I'm going with weak hurricane for a really short time on the 10th. But thats my option.


By review of the Hrd/recon plus dry air I'v lowered Arlene to a strong tropical storm.

[HURAKAN]

I think you are right, and I hope they revise all the obtained information and on the Best-track upgrade officially the system to hurricane like happened in 2003 with Erika and in 2004 with Gaston.

[Derek Ortt]

there is absolutely no data that indicates this was a hurricane.

75KT at 850mb equates to 60KT at the surface, not 65KT

Also, SFMR never indicated a hurricane.

Arlene was not a hurricane. Winds may be lowered slightly on BT to 55KT as the 70 m.p.h. winds likely did not make it to the surface

[senorpepr]

I will agree. I really doubt Arlene was a hurricane. Recon didn't find anything that supported hurricane strength and most of the data available shown that a majority of the winds at flight level were having a hard time mixing to the surface.


(Then again... you have some idiots [notsogreatone] that believe this was an 80mph hurricane... which was FAR from the truth.)

[recmod]

Recon shown that winds where at flight level 75 knots=86 mph or reduced 90 percent to 75 mph. Which makes this a hurricane.

Many advisory discussions from the NHC indicated that these flight level winds were not mixing down to the surface:

5am June 10 Discussion:
"FLIGHT-LEVEL WINDS OF 56
KT AT 850 MB NEAR THE ISLE OF YOUTH. HOW MUCH OF THIS WIND IS
REACHING THE SURFACE IS QUESTIONABLE...AS THE CONVECTION IN THE
AREA IS SOMEWHAT ISOLATED AND THE ISLE OF YOUTH REPORTED 20 KT
WINDS AT 06Z. HOWEVER...THESE FLIGHT-LEVEL ARE STRONG ENOUGH TO
JUSTIFY INCREASING THE INITIAL INTENSITY TO 40 KT"

11am June 10 Discussion:
"AN AIR
FORCE RESERVE HURRICANE HUNTER AIRCRAFT REPORTED A MAXIMUM 850 MB
FLIGHT LEVEL WIND OF 64 KT ABOUT 110 NM NORTHEAST OF THE CENTER AT
1130Z. THIS CORRESPONDS TO ABOUT 50 KT AT THE SURFACE...WHICH IS
THE BASIS FOR THE ADVISORY INTENSITY"

5pm June 10 Discussion:
"AND 850 MB FLIGHT
LEVEL WINDS RECENTLY PEAKED AT 69 KT. ON THIS BASIS...THE INITIAL
INTENSITY IS ADJUSTED UPWARD TO 55 KT"

11pm June 10 Discussion:
"THE INITIAL INTENSITY OF 60 KT IS
BASED ON 850 MB FLIGHT-LEVEL WINDS OF 75 KT IN THE NORTHEAST QUAD"


5am June 11 Discussion:
"MAXIMUM
FLIGHT-LEVEL WINDS OF 69 KT WELL NORTHEAST OF THE CENTER AT 850
MB...ALONG WITH A MINIMUM CENTRAL PRESSURE OF 993 MB. COMPARISON
OF AIRCRAFT WINDS WITH BUOYS AND C-MAN STATIONS SOUTH OF
APALACHICOLA SUGGESTS THE FLIGHT-LEVEL WINDS ARE NOT BEING MIXED TO
THE SURFACE AT THE NORMAL 70-80 PERCENT VALUES...AT LEAST AT THAT
DISTANCE FROM THE CENTER. THE MAXIMUM SUSTAINED WINDS WILL REMAIN
60 KT FOR THIS ADVISORY...ALTHOUGH THIS MIGHT BE A BIT GENEROUS"

Matt used 90% as the reduction from flight level to surface wind values...which is the number I also have heard is used (wasn't this much of the basis for upgrading Andrew to a Cat 5 storm??) But the NHC advisory clearly states the normal ratio is 70-80% of 850mb flight level measurment. Here's a question maybe Derek or one of the pro mets can answer...is the 90% reduction based on a different flight level measurement..ie...closer to the surface??
--Lou

[Thunder44]

At one point Arlene had a pressure of 989 MB, which is more consistent with a minimal hurricane. But I don't think it ever had 74mph+ winds at the surface. There weren't any obs that even suggested that. I think Arlene made landfall with sustained winds closer to 50mph.

[Lowpressure]

It may have been close at flight level. But, as a few have pointed out the NHC did not believe the strongest winds were making it to the surface. No bouy ever hit 75 mph, and land observation were not even close. I think the pressure generally agreed upon as a minimal Hurricane is 984mb.

[MGC]

Arlene was not close to being a hurricane. No surface observation was close. IMO, Arlene was more ST at the begining than tropical as the strongest winds were well removed from the circulation center. Arlene was falling apart as she approached the coast. She suffered from shear and dry air durning nearly the entire track.......MGC

[dhweather]

Arlene was not close to being a hurricane. No surface observation was close. IMO, Arlene was more ST at the begining than tropical as the strongest winds were well removed from the circulation center. Arlene was falling apart as she approached the coast. She suffered from shear and dry air durning nearly the entire track.......MGC

bingo

[wxman57]

As was pointed out, your flight level to sfc wind conversion was wrong. While an 80-90% conversion may be ok for 700mb (10,000 ft), the plane was at 1500 ft - the peak wind height (typically) in a tropical storm. So the convesion factor is more like 70-80%, as indicated by James Franklin in this paper:

http://www.nhc.noaa.gov/aboutwindprofile.shtml

I might add, that not all tropcial systems are alike in terms of their vertical wind fields. Clearly, Arlene's winds were much lower at the surface than a typical tropical storm. So the conversion factor from 850 mb with Arlene may have been closer to 60-70%. It wasn't even close to a hurricane at any time.

[LarryWx]

At one point Arlene had a pressure of 989 MB, which is more consistent with a minimal hurricane. But I don't think it ever had 74mph+ winds at the surface. There were obs that even suggested that. I think Arlene made landfall with sustained winds closer to 50mph.

Regarding 989 perhaps being a bit low for a TS, I'm wondering if the ambient pressure was below normal. If so, it could easily mean that a lower than normal pressure would be needed to make it a hurricane. Anyone know or have an opinion? Thanks.

[Brent]

I don't believe it was a hurricane either... 989 is actually a couple of MB above what is widely believed to be a hurricane(987 mb). Also the fact that the convection was pretty weak means 60 kt was probably a little high. I'm thinking it might even be revised downward on the prelim report.

[Lowpressure]

This dicussion makes me think about all parameters needing to be met. Such as, all of the criteria to make a thunderstrom severe, or a smowstorm a blizzard. I do not think all criteria was here for Arlene, pressure was close but system never verticle stacked storms never consolidated near the center and she ate dry air here whole life. It goes back to our earlier discussion when we debated whether she was really tropical with storms 75 miles or so from the center.

[Matt-hurricanewatcher]

I also believe because of the dry air that was moving into the system. That the winds might not made it all the way to the surface. I said that quite a few times over the last few days...But I also believe that a few small drop sounds doe's not look at a 250 nmi wide storm fully. I know 75 knots is at 80 percent around 60 knots. In after I made this I did look at the maps at Hrd that shown it to be weaker. Of course I knew people would not be happy.


I might lower it to around 55 knots based on the recon/dry air. In the new hrd report. This is how we all learn for doing it then redoing it.

[Matt-hurricanewatcher]

By reviewing the HRD wind maps, And recon...I'v down graded it to 60 knots max.

[Swimdude]

I'm not sure any of us can simply say that Arlene was a hurricane by our own judgment. The Recon. planes tell us what there is to know. Of course, it would be much more exciting and rare to have a hurricane begin the season; in June, at that.

Patience!

[Matt-hurricanewatcher]

So no one likes it This is how I learn.

[Swimdude]

I think we agree with you - on everything except the statement of Arlene being a hurricane. Everything else is done well. =)

[Brent]

No... she wasn't a hurricane. Recon winds weren't strong enough using the normal conversion, and with the convection weak, the 60 kt was defintely generous.