"Naked" Swirls

[StarmanHDB]

Back on July 15, a close friend pointed out what he termed a "naked swirl" floating over the Atlantic west of Cape Verde. This naked swirl eventually became Tropical Storm Bonnie. Since that time, I've been staring at so many satellite loops that all I see are counterclockwise rotating swirls! All of that said, what is currently swirling around near 10N, 42W? At what point does one need to start paying attention to these not-so-obvious tropical features?

Looking forward to reading all responses!


http://www.ssd.noaa.gov/goes/east/catl/flash-vis.html

[A1A]

I believe you are talking about ULL (Upper Level Low) that can look impressive but rarely create significant weather activity at mid and lower levels.

[A1A]

I guess I stand corrected about the "rarely" - looks like these ULLs are impacting South Central Texas this week . . .



.PREV DISCUSSION... /ISSUED 330 AM CDT MON JUL 26 2010/

DISCUSSION...
THIS MORNING THE TUTT LOW WAS LOCATED OVER NORTH TEXAS DRIFTING
WESTWARD. THE EASTERN HALF OF OUR CWA WILL BE ON THE INFLOW SIDE
OF THE FEATURE TODAY. THUS THE BEST CHANCE FOR SHOWERS AND
THUNDERSTORMS WILL BE SOUTH AND EAST OF THE I-35 CORRIDOR WHERE
THE SEA BREEZE BOUNDARY WILL ASSIST IN INITIATING CONVECTION.
AFTERNOON TEMPS WILL BE AT OR SLIGHTLY BELOW NORMAL...DEPENDENT
ON WHERE THE PCPN OCCURS. CONVECTION WILL WANE OVERNIGHT WITH THE
LOSS OF DAYTIME HEATING.

ANOTHER TUTT LOCATED OVER THE EASTERN GULF IS MOVING WESTWARD. THIS
FEATURE COMBINED WITH THE TUTT OVER NORTHWEST TEXAS WILL ALLOW A
PERSISTENT AND DEEP FLOW OF TROPICAL GULF MOISTURE TO OVERSPREAD
SOUTH CENTRAL TEXAS TUESDAY AND WEDNESDAY. PWS WILL BE ON THE
INCREASE...APPROACHING 2.25 INCHES. PWS OF TWO INCHES IS THE
THRESHOLD FOR TROPICAL DOWNPOURS FOR SOUTH CENTRAL TEXAS AND HAVE
INCLUDED LOCAL HEAVY RAINFALL IN THE FORECAST FOR TUESDAY AND
WEDNESDAY. THE THREAT WILL BE MINOR FLOODING OF URBAN AREAS AND
SMALL CREEKS AND STREAMS. LOCALIZED RAINFALL AMOUNTS EACH DAY WILL
RANGE FROM ONE TO THREE INCHES. THESE CONCERNS WILL BE ADDRESSED
IN THE HAZARDOUS WEATHER OUTLOOK. WE ALSO WILL GOING HIGHER THAN
THE HPC GUIDANCE FOR QPF TUESDAY AND WEDNESDAY. AFTERNOON TEMPS
WILL BE BELOW AVERAGE DUE TO THE INCREASED CLOUD COVER ASSOCIATED
WITH THE ANTICIPATED SHOWERS AND THUNDERSTORMS.

THURSDAY WILL BE THE TRANSITIONAL DAY WITH ONLY A SLIGHT CHANCE OF
SHOWERS AND THUNDERSTORMS DUE TO RESIDUAL GULF MOISTURE. THE UPPER
LEVEL RIDGE WILL BUILD WESTWARD INTO SOUTH CENTRAL TEXAS ON FRIDAY
BRINGING AND END TO OUR RAIN CHANCES. THE UPPER RIDGE WILL STRENGTHEN
ACROSS THE REGION OVER THE WEEKEND. AFTERNOON TEMPERATURES WILL BE
ON THE RISE OVER THE WEEKEND DUE TO THE RIDGING ALOFT...HOWEVER
THE TEMPERATURES WILL STILL BE AROUND THE SEASONAL NORMAL.

[rockyman]

When I see a swirl, I look at thes maps below. In a nutshell (though it's way more complicated than what I'm about to write)...if the swirl shows up in the lower levels, then it could develop into a tropical system. If the swirl only shows up in the upper levels, then it's an upper low that won't (at least in the short term) develop into a tropical system. If it shows up in both levels, it could be a "deep cold core low" that could acquire some tropical characteristics and become a "hybrid, subtropical system".

Lower level:
http://cimss.ssec.wisc.edu/tropic2/real ... oom=&time=

Upper level:
http://cimss.ssec.wisc.edu/tropic2/real ... oom=&time=

[wxman57]

Back on July 15, a close friend pointed out what he termed a "naked swirl" floating over the Atlantic west of Cape Verde. This naked swirl eventually became Tropical Storm Bonnie. Since that time, I've been staring at so many satellite loops that all I see are counterclockwise rotating swirls! All of that said, what is currently swirling around near 10N, 42W? At what point does one need to start paying attention to these not-so-obvious tropical features?

Looking forward to reading all responses!

http://www.ssd.noaa.gov/goes/east/catl/flash-vis.html

Bonnie reached the coast of Africa late on July 13th as a very potent tropical wave with plenty of convection (thunderstorms). As with many such strong tropical waves, it had a mid level circulation as well as a weak surface circulation. Once it moved offshore, the convection died off fairly quickly, like with so many such strong waves early in the season. This left that "naked swirl" of low clouds that your friend pointed out to you.

But the wave still lacked a great deal of energy, even though dry, sinking air was inhibiting thunderstorm development. That's why we need to track all tropical waves across the Atlantic, even those with few thunderstorms. Because once they reach a favorable environment they can develop.

However, not all such swirls that you see on the satellite loops are development candidates. Many are simply upper-level features located in high-shear regions.