Yasi vs. Larry: What the Satellite Saw

John Knaff

NOAA/NESDIS –RAMMB

Fort Collins, Colorado

Overview

TC Larry (2006)• Landfall 20 March

– South of Innisfail– 95km S. of Cairns– 940 hPa (best track, BoM)– 959 hPa (measured, 2 -4 h post

landfall)– 100kt (10-min, BoM)– 240 km/h gusts, BoM– 115 kt (1-min, JTWC, best)– 90 n.mi Gale force wind– 30 n.mi Hurricane force wind– 4.9 meter inundation – Average length track

TC Yasi (2011)• Landfall 3 February

– near Mission Beach– 138km S. of Cairns– 929 hPa (Tully Sugar Mill) – 110 kt (10-min, BoM)– 135 kt (1-min, JTWC)– 200 + n.mi Gale force winds– 60 + n.mi Hurricane force

winds– 5 meter tidal surge – Fast translation– Long track

Larry Intensity (objective & subjective)

Digital Dvorak

Larry Landfall Intensity

Best track

BoM• 100kt / 115 kt• 940 hPa (table),959 hPa

observed• Gusts to 240 km/h

damage derived

JTWC• 100 kt / 115 kt

Translation 270/13 kt

Imagery

Subjective T-numbers of 6.5 (127 kt) are possible. 6-hour average close to 6.0

Eyewall Replacement?

Microwave imagery (NRLMRY) IR imagery suggests

• Possible eyewall replacement starting at ~ 16-17 UTC

• Microwave suggest two eyewalls a little earlier at 1541 UTC

Eyewall Replacement?

89 GHz 1700 UTC Radar Composite at 14 UTC

Landfall

• Larry appears to have experienced a quick eyewall replacement just prior to landfall– Double eyes evident in MI from 16 UTC on– Both radar and microwave imagery suggest a

larger eye at landfall… replacement complete.

Larry was a small storm

Operational Wind Radii 12-h average IR image

Area ~ 2560 km x 1920 km

reanalysis of Satellite-based Sfc Winds

Pressure-Wind

• ~950-955 hPa• 90-110 nmi R34• 13 kt translation• 18S latitude

Yields a 100/115 kt intensity.

Yasi Intensity

Digital Dvorak

Yasi Landfall Intensity

Best track

BoM• 110 kt / 125 kt• 929 hPa, observed• …Gusts 280 km/h

JTWC• 120kt / 135 kt

Translation 250/17 kt

Imagery

Subjective T-numbers of 7.0 (140) are possible, but not at the times of the fixes 6-h average close to 6.6

Landfall

• Yasi experienced only slight structural changes as it approached the coast– Unanticipated left turn delayed landfall– Large storm, stable eye size

Larry was a small storm

Operational Wind Radii 12-h average IR image

Area ~ 2560 km x 1920 km

Real-time analysis of Satellite-based Sfc Winds

Pressure-Wind

• ~930 hPa• 200-230 nmi R34• 17 kt translation• 18S latitude

Yields a 115/130 kt intensity.

Summary what the satellite saw

Larry• Small storm

– Average R34 90 to 110 nmi– Short lifetime

• Major hurricane at landfall– Subjective Tnums of max=6.5 (127kt),

mean=6.0 (115 kt)– Digital Dvorak T=7.5 (155 kt)– ODT N/A

• Eyewall cycle completing at landfall• Factors (increase dvorak)

– Translation at 13 kt (+)– Latitude =18S (-)– 12-h trend up (+)– small (+)

Yasi• Larger storm

– Average R34 200 to 230 nmi– Started large and had a long track.

• Major Hurricane at landfall– Subjective Tnums of max=7.0 (140

kt), mean=6.6 (130 kt)– Digital Dvorak T = 7.5 (155 kt)– ODT T=6.9 -7.0– Structure stable at landfall– Factors (increase Dvorak)

• Translation 17 kt (+)• Latitude = 18S (-)• 12-h trend slightly up (+)• Large/average (-)

Conclusion at Landfall

Larry• Intensity should be close to

100/115 kt based on pressure, translation, latitude, size and damage– Dvorak estimates too high,

especially Digital– AMSU estimates too low

• Satellite based size estimates seem able to conclude Larry was small

• Eyewall cycle completed around time of landfall

Yasi• Intensity should be close to

115/130 kt based on pressure, translation, latitude, size and damage– Dvorak estimates too high,

particularly Digital, ADT– AMSU estimates too low, but better

• Satellite based size estimates seem able to conclude Yasi was average/large

• Showed that Yasi’s structure was fairly stable as it rapidly made landfall.

JTWC’s Track/Intensity/Size