ATL: ANA - Post-Tropical - Discussion

[Subtrop]

SUBJ/TROPICAL CYCLONE FORMATION ALERT (90L)//
WTNT21 KNGU 202200
RMKS/1.FORMATION OF A SIGNIFICANT TROPICAL CYCLONE IS POSSIBLE WITHIN
100 NM EITHER SIDE OF A LINE FROM 34.4N 53.7W TO 36.3N 54.0W
WITHIN THE NEXT 24 HOURS. AVAILABLE DATA DOES NOT JUSTIFY
ISSUANCE OF NUMBERED TROPICAL CYCLONE WARNINGS AT THIS TIME.
WINDS IN THE AREA ARE ESTIMATED TO BE 40 TO 50 KNOTS. METSAT
IMAGERY AT 201800Z INDICATES THAT A CIRCULATION CENTER IS LOCATED
NEAR 34.4N 53.7W. THE SYSTEM IS MOVING NORTH-NORTHWESTWARD AT 05
KNOTS.
2.REMARKS: A NON-TROPICAL LOW PRESSURE SYSTEM IS SITUATED ABOUT 670
NM NORTHEAST OF BERMUDA. SATELLITE DERIVED WIND DATA INDICATE THAT
THE SYSTEM IS PRODUCING GALE-FORCE WINDS THAT EXTEND A FEW HUNDRED
MILES NORTH OF THE SURFACE CENTER. SHOWER AND THUNDERSTORM ACTIVITY
IS GRADUALLY BECOMING BETTER ORGANIZED AND THIS CONVECTIVE TREND
SHOULD CONTINUE THROUGH TONIGHT AND FRIDAY AS THE SYSTEM MOVES OVER
WARMER OCEANIC TEMPERATURES. CONSEQUENTLY, A SUBTROPICAL DEPRESSION
OR STORM IS LIKELY TO FORM DURING THE NEXT 24 HOURS AS THE LOW MOVES
WESTWARD TO WEST-SOUTHWESTWARD, REMAINING WELL TO THE NORTHEAST OF
BERMUDA.
3. THIS ALERT WILL BE REISSUED, UPGRADED TO WARNING OR CANCELLED BY
212200Z.//
BT
#0001
NNNN

[Nancy Smar]

A developing low pressure to the east is expected to drift towards the area tomorrow and through the weekend bringing increasing winds, shower activity, and cloud cover. We continue to monitor this low for possible subtropical development. Regardless of development, the low will drive periods of wet weather into the area from Friday into the weekend. A tropical storm watch is now in effect.

Tropical Storm Watch
Updated: 4:30 pm Thursday, May 20, 2021
Additional Information:
A potential tropical or subtropical disturbance is developing approximately 600 nm east of Bermuda, but has not formed yet. A Tropical Storm Watch has been issued, to cover the potential for sustained winds reaching 35 knots and seas exceeding 12 feet offshore on Friday. For more detail, please review the Marine Forecast. Once formal advisories begin, BWS will start issuing Tropical Update Bulletins with more details about track and intensity.

[Hammy]

A developing low pressure to the east is expected to drift towards the area tomorrow and through the weekend bringing increasing winds, shower activity, and cloud cover. We continue to monitor this low for possible subtropical development. Regardless of development, the low will drive periods of wet weather into the area from Friday into the weekend. A tropical storm watch is now in effect.

Tropical Storm Watch
Updated: 4:30 pm Thursday, May 20, 2021
Additional Information:
A potential tropical or subtropical disturbance is developing approximately 600 nm east of Bermuda, but has not formed yet. A Tropical Storm Watch has been issued, to cover the potential for sustained winds reaching 35 knots and seas exceeding 12 feet offshore on Friday. For more detail, please review the Marine Forecast. Once formal advisories begin, BWS will start issuing Tropical Update Bulletins with more details about track and intensity.

Has a tropical storm watch ever been issued prior to advisories being initiated?

[JW-_-]

http://weather.bm/tools/graphics.asp?na ... LITE&user=

[aspen]

90L looks to be in the process of detaching from the front and consolidating. The 00z best track puts it at 50 kt, so if it becomes Ana, it’s starting off at a good intensity. 90L’s winds should decrease as it becomes subtropical but it’ll still be a better starting off point than TD-force tropical waves.

I’d say Ana’s maximum potential intensity as a named TC/STC is 50-55 kt.

[cycloneye]

50kts.

90L INVEST 210521 0000 34.9N 55.0W ATL 50 1004

[JW-_-]

[cycloneye]

Showers and thunderstorms associated with a non-tropical low
pressure area centered about 450 miles east-northeast of Bermuda
have become better organized during the past several hours. The
low has not yet acquired subtropical storm characteristics.
However, if current trends continue advisories could be initiated
on the system later today or tonight as it moves westward
to west-southwestward to the northeast of Bermuda. Subsequently,
the low is forecast to move northeastward into a more hostile
environment by Saturday night or Sunday. Additional information on
this low pressure area can be found in High Seas forecasts issued by
the NOAA Ocean Prediction Center and forecast products, including a
tropical storm watch, issued by the Bermuda Weather Service.
* Formation chance through 48 hours...high...90 percent.
* Formation chance through 5 days...high...90 percent.

[Hypercane_Kyle]

Looking very good. Fully expecting STS Ana by 5 PM Eastern.

[aspen]

Looking very good. Fully expecting STS Ana by 5 PM Eastern.

https://i.imgur.com/FHSSBTa.jpg

Convection could be better, but it seems to be fully detached now and ready to become a STC.

[DorkyMcDorkface]

I'd definitely say this is classifiable now...

[tolakram]

SLIDER floater
https://rammb-slider.cira.colostate.edu/?sat=goes-16&sec=mesoscale_01&x=1127&y=800&z=2&angle=0&im=12&ts=1&st=0&et=0&speed=130&motion=loop&maps%5Bborders%5D=white&lat=0&p%5B0%5D=band_02&opacity%5B0%5D=1&pause=0&slider=-1&hide_controls=0&mouse_draw=0&follow_feature=0&follow_hide=0&s=rammb-slider&draw_color=FFD700&draw_width=6

COD:
https://weather.cod.edu/satrad/?parms=meso-meso1-02-24-0-100-1&checked=map&colorbar=undefined

[kevin]

Looks pretty good right now.

[Shell Mound]

Based on satellite, this clearly appears to be non-frontal at this stage and, given sufficient organisation, is already STS Ana, in my view. Upgrade at 15:00 UTC?

[Sciencerocks]

Looks like Ana to me!

[lrak]

Surf!!!

[lrak]

Surf!!!

ooops...

[Shell Mound]

https://imagizer.imageshack.com/img924/674/wGKcCZ.gif

Looks like Ana to me!

I’m a little surprised that the NHC didn’t upgrade 90L at STS Anna at 11:00 a.m. EDT (15:00 UTC). Does anyone know why? Convection seems sufficient.

[Sciencerocks]

https://imagizer.imageshack.com/img924/674/wGKcCZ.gif

Looks like Ana to me!

I’m a little surprised that the NHC didn’t upgrade 90L at STS Anna at 11:00 a.m. EDT (15:00 UTC). Does anyone know why? Convection seems sufficient.

I am guessing that they're waiting for solid evidence for a warm core as convection has only been building around the LLC for the past 8-9 hours and also for solid data for a complete detachment for the frontal structure. I am guessing they'll pull the trigger at 5pm est.

[aspen]

There is a very clear LLC, but not much convection at all.