Why does the forward speed of a storm effect Dvorak estimate

[Just Joshing You]

Reading through past advisories on Wilma, I see Stewart saying the following:

"IN ADDITION... DVORAK
T-NUMBERS FROM TAFB AND SAB ARE T4.5/77KT. ADDING THE FORWARD SPEED
OF WILMA TO THE T-NUMBERS SUPPPORTS AN INTENSITY OF ABOUT 110 KT."

http://www.nhc.noaa.gov/archive/2005/di ... .040.shtml?


Why?

[AJC3]

Reading through past advisories on Wilma, I see Stewart saying the following:

"IN ADDITION... DVORAK
T-NUMBERS FROM TAFB AND SAB ARE T4.5/77KT. ADDING THE FORWARD SPEED
OF WILMA TO THE T-NUMBERS SUPPPORTS AN INTENSITY OF ABOUT 110 KT."

http://www.nhc.noaa.gov/archive/2005/di ... .040.shtml?


Why?

Here is a larger portion of the TCD which pretty much answers the intensity question...

WILMA'S EYE HAS BECOME BETTER DEFINED DURING THE PAST 6 HOURS... AND
THE DIAMETER HAS DECREASED FROM 60 NMI DOWN TO 40 NMI. THE EYEWALL
CONVECTION HAS ALSO INCREASED WITH CLOUD TOP TEMPERATURES OF -75 TO
-80C NOTED IN SATELLITE IMAGERY. AT 24/2001Z... AN AIR FORCE RECON
AIRCRAFT REPORTED 136-KT 850 MB FLIGHT-LEVEL WINDS IN THE SOUTH
QUADRANT. SINCE THAT TIME... BOTH THE EYE AND EYEWALL CONVECTION
HAVE IMPROVED SIGNIFICANTLY... AND USING AN 80 PERCENT REDUCTION
FACTOR YIELDS ABOUT 109 KT SURFACE WINDS. IN ADDITION... DVORAK
T-NUMBERS FROM TAFB AND SAB ARE T4.5/77KT. ADDING THE FORWARD SPEED
OF WILMA TO THE T-NUMBERS SUPPPORTS AN INTENSITY OF ABOUT 110 KT.

THE INITIAL MOTION ESTIMATE IS NOW 045/41

Dvorak intensity estimates do not take into account the forward speed of a storm. It is merely an estimate of it's intensity based upon it's satellite presentation. What Stacy did here was to look at the total picture. Wilma's intensity estimate of 110kt was supported by both recon observations as well as the satellite intensity estimate coupled with its forward speed.

[Just Joshing You]

So if Wilma was stationary, the wind speeds would have been lower?

[AJC3]

So if Wilma was stationary, the wind speeds would have been lower?

Assuming all other things about the storm, structrually speaking, were identical at the time, then yes. Recon would have found lower peak winds and Wilma's MSW would have been lower.