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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