ATL LAURA: Tropical Storm - Discussion

[RL3AO]

AL, 12, 2008093000, , BEST, 0, 386N, 484W, 50, 995, SS

No change.

[cycloneye]

Part of the 11 PM Discussion about why they haved not changed yet to fully tropical.

LAURA IS STILL
VERY MUCH INVOLVED WITH AN UPPER-LOW...WHICH IS A DEFINING
CHARACTERISTIC OF A SUBTROPICAL STORM. I'M NOT INCLINED TO CALL
THIS THING FULLY TROPICAL UNTIL IT DOES A BETTER JOB OF ERODING THE
UPPER LOW. OVER THE NEXT DAY OR SO THE UPPER-LOW IS EXPECTED TO
WEAKEN AS LAURA MOVES INTO THE WESTERLIES...AND LAURA STILL COULD
BECOME A TROPICAL CYCLONE BEFORE SEA SURFACE TEMPERATURES DROP
DRAMATICALLY ALONG THE FORECAST TRACK IN ABOUT 18 HOURS

http://asp1.sbs.ohio-state.edu/tropical ... 93002.disc

[HURAKAN]

"this thing" says Franklin.

Our "poof" designation is not looking bad after all.

[Matt-hurricanewatcher]

Looks to be fully tropical with convection blowing over the center...Also the cirulation has grown to a tropical cyclone size,,,which means the wind field is likely more inline with a fully tropical cyclone to. Very likely it is upgradeable.

[Matt-hurricanewatcher]

000
WTNT42 KNHC 300831
TCDAT2
SUBTROPICAL STORM LAURA DISCUSSION NUMBER 5
NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL AL122008
500 AM EDT TUE SEP 30 2008

LAURA CONTINUES TO PRODUCE CONVECTIVE BANDS AROUND THE CENTER...WITH
CLOUD TOPS COLDER THAN -60C TO THE NORTH AND NORTHEAST OF THE
CENTER. A RECENT AMSU OVERPASS SHOWS A WELL-DEFINED MID/UPPER-
LEVEL WARM CORE...SUGGESTING THAT LAURA IS BECOMING MORE TROPICAL.
HOWEVER...WATER VAPOR IMAGERY SHOWS THAT THE SYSTEM IS STILL
STRONGLY INVOLVED WITH AN UPPER-LEVEL LOW. ALSO...THERE ARE NO
SIGNS OF THE ANTICYCLONIC UPPER-LEVEL OUTFLOW CHARACTERISTIC OF A
TROPICAL CYCLONE. BASED ON THIS...THE SYSTEM IS STILL DESIGNATED A
SUBTROPICAL STORM.


This must something new, because I've seen the nhc upgrading to tropical storms before with a upper ULL on top of them. Never can know what the nhc will do. I disagree because if it has a deep enough warm core to be a tropical storm=tropical storm.

[Chacor]

This must something new, because I've seen the nhc upgrading to tropical storms before with a upper ULL on top of them. Never can know what the nhc will do. I disagree because if it has a deep enough warm core to be a tropical storm=tropical storm.

ALSO...THERE ARE NO
SIGNS OF THE ANTICYCLONIC UPPER-LEVEL OUTFLOW CHARACTERISTIC OF A
TROPICAL CYCLONE.

I think they're justified in keeping it subtropical. Doesn't hurt to change it in post-analysis anyway if they deem it to have been tropical earlier, as it won't make any appreciable difference.

[Matt-hurricanewatcher]

This must something new, because I've seen the nhc upgrading to tropical storms before with a upper ULL on top of them. Never can know what the nhc will do. I disagree because if it has a deep enough warm core to be a tropical storm=tropical storm.

ALSO...THERE ARE NO
SIGNS OF THE ANTICYCLONIC UPPER-LEVEL OUTFLOW CHARACTERISTIC OF A
TROPICAL CYCLONE.

I think they're justified in keeping it subtropical. Doesn't hurt to change it in post-analysis anyway if they deem it to have been tropical earlier, as it won't make any appreciable difference.

I've seen subtropical to tropical like systems like this get upgraded for just finding a deep enough warm core, also straight to tropical...I just never seen it before that it has to have a anticyclone over it. We will have to wait for post season to see like you say.

[littlevince]

I've seen subtropical to tropical like systems like this get upgraded for just finding a deep enough warm core, also straight to tropical...I just never seen it before that it has to have a anticyclone over it. We will have to wait for post season to see like you say.

By coincidence a few days ago I read some things about the Hurricane Vince and the 4-5 October 2005 Unnamed Subtropical Storm and they also refer the upper-level anticyclone in their post-season report.

The presence of the warm core at 200 mb suggests the possibility that the storm may have
become fully tropical. However, the warm core is indistinct in channel 8 imagery
(corresponding to approximately 100 mb; not shown), and satellite cloud-motion winds (not
shown) indicate the presence of an upper-level trough over the storm near the time of peak
intensity rather than the upper-level anticyclone that would be expected for a tropical cyclone.
Additionally, the radius of maximum winds based on surface observations was large, about 75 n
mi. These factors argue in favor of a subtropical rather than a tropical classification

Tropical Cyclone Report Unnamed Subtropical Storm 4-5 October 2005
http://www.nhc.noaa.gov/pdf/TCR-AL212005_Unnamed.pdf

BTW, in the last LAURA discussion and in the report i cited above, they talk about the AMSU (Advanced Microwave Sounding Unit) on the NOAA polar-orbiting satellite to confirm the presence of warm-core.
Do we (general public) have access to this product ?

[Matt-hurricanewatcher]

To my eyes this thing is now a tropical storm, with a soild layer of convection over 70 percent of the cirulation. It should be short lived. Lets see if they go for it at 11am.

[cycloneye]

12:00 UTC Best Track says its now a Tropical Storm.

AL, 12, 2008093012, , BEST, 0, 406N, 489W, 50, 996, TS,

[HURAKAN]

30/1145 UTC 40.5N 48.6W ST2.5 LAURA -- Atlantic Ocean

[HURAKAN]

Laura is a lot smaller than when classified.

[HURAKAN]

Best track 12z:

AL, 12, 2008093012, , BEST, 0, 406N, 489W, 50, 996, TS

Hello Tropical Storm Laura

[HURAKAN]

Tropical Storm Laura

[Just Joshing You]

While I understand it is a mere formality, it's not a TS until the NHC says so!

[HURAKAN]

While I understand it is a mere formality, it's not a TS until the NHC says so!

That's why I say "based on the Best Track." The NHC has the final word.

[RL3AO]

While I understand it is a mere formality, it's not a TS until the NHC says so!

That's why I say "based on the Best Track." The NHC has the final word.

Well, the NHC is the best track, but you mean wait for the advisory.

[HURAKAN]

318
WTNT22 KNHC 301432
TCMAT2
TROPICAL STORM LAURA FORECAST/ADVISORY NUMBER 6
NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL AL122008
1500 UTC TUE SEP 30 2008

$$
FORECASTER BERG/PASCH

[Chacor]

The best-track doesn't always reflect what happens at advisory, since they are technically three hours apart.

At any rate:

...LAURA BECOMES TROPICAL...BUT NOT FOR LONG...

[HURAKAN]