The Controversy Regarding HS3 Surface Pressure Observations During The Rapid Intensification of Edouard on September Scott Braun NASA/GSFC

Controversy over Dropsonde Data During Sept Flight NHC night shift rejected HS3 dropsonde measurements of surface pressure during flight Morning shift reversed decision, upgraded storm intensity However, final storm report did not accept HS3 central pressure estimates

NOAA P-3 and GH MSLP Measurements Date/TimeLocation relative to center Psfc (mb) Wind Speed (kt) Estimated MSLP(mb)** P3 14/1500Eye center9834 P3 14/1707NE GH 14/2103N GH 15/0031N GH 15/0034S GH 15/0217W_SW GH 15/0428N GH 15/0552NW **Surface pressure adjusted 1 mb for each 10 kt Adjusted Psfc derived from lowest altitude pressure measurement

GH Surface Pressures and Winds Surface PressureSurface Winds Pressures and winds appear consistent with strong storm Wind barbs show storm-relative winds

NHC Final MSLP Time Series

P-3 drops North-side GH drops South-side GH drops North-side GH drops

The Beginning of a Convective Burst 9/ UTC 9/ UTC 9/ UTC9/ UTC Convective burst began near 1045 UTC on NW side of eye Over time, CB cloud shield expanded and moved to southern side As cloud shied expanded, the eye was obscured

The First P-3 Drop 9/ UTC 9/ UTC 9/ UTC NOAA P-3 dropsonde reported MSLP of 983 mb, 2 m s -1 surface wind The eye is still obscured by CB cirrus shield

Gradual Formation of a New Eye 9/ UTC9/ UTC 9/ UTC9/ UTC CB cloud shield continues to circle around southern to eastern sides New eye begins to for by ~1645 UTC 9/ UTC

Last P-3 Drop 9/ UTC 9/ UTC NOAA P-3 dropsonde reported MSLP of 984 mb, 41 m s -1 surface wind. Suggests possible MSLP closer to 976 mb, a 7 mb decrease from the dropsonde 2 hours before. Very small, well-defined eye present by 1715 UTC

GH dropsonde at 2103 UTC reported MSLP of 972 mb, 46 m s -1 (89 kt) surface wind. Suggests possible MSLP closer to 963 mb, a 13 mb decrease from the P-3 dropsonde 4 hours before. 9/ UTC 1 st GH “Eye” Drop

2 nd GH Eye Drop GH dropsonde at 0031 UTC reported MSLP of 967 mb, 44 m s -1 (86 kt) surface wind. Suggests possible MSLP closer to 958 mb, a 5 mb decrease from the GH dropsonde 3.5 hours before.

2 nd GH Eye Drop GH dropsonde at 0031 UTC reported MSLP of 967 mb, 44 m s -1 (86 kt) surface wind. Suggests possible MSLP closer to 958 mb, a 5 mb decrease from the GH dropsonde 3.5 hours before

Edouard Appears to Undergo an ERC 9/ UTC9/ UTC9/ UTC 9/ UTC9/ UTC9/ UTC

Storm Evolution and Intensity Change CB begins Small eye forms Small eye begins breakdown Large eye begins to form >3 hPa/h pressure fall

Is the Observed Rate of Pressure Fall Likely? Used HURDAT data from to compute 6-h pressure changes for all named storms during mid-August to mid-October Here expressed as 1-h pressure change rates and shown as a function of max. wind speed at time of pressure change 3 hPa/h rates only observed for storms that go on to become Cat 4-5

Is the Observed Rate of Pressure Fall Likely? Max wind change vs min SLP change 25 hPa/9.5 h (2.6 hPa/h) pressure drop implies ~31 kt increase in max winds Storm max wind should have increased from ~72 to ~103 kt (Cat 3) 2103Z Sep 14 sounding had 89 kt (46 m s -1 ) NHC had storm as 80 kt (strong Cat 1)

Is the Observed Rate of Pressure Fall Likely? Max wind change vs min SLP change 22 hPa/9.5 h (2.3 hPa/h) pressure drop implies ~28 kt increase in max winds Storm max wind should have increased from ~72 to ~100 kt (Cat 3) 2103Z Sep 14 sounding had 89 kt (46 m s -1 ) NHC had storm as 80 kt (strong Cat 1)

Conclusions P-3 and GH dropsondes were consistent with satellite indications of rapid intensification Several drops indicated likely central pressures in the 960’s mb Magnitude of pressure drop appears too intense (typical of Cat 4-5 storms and very rare) Do we declare that this was an unusual Cat 3 storm or re-examine the validity of the measurements? Is there a region of ~51 m s -1 somewhere in here?

Extra slides

15 Past Storms With  P/  T≤3mb/h Anita (1977, 5)-18mb/6h, -32mb/12h in consecutive times Gloria (1985, 4)-24mb/6hsecond period of -30mb/12h Gilbert X 2 (1988, 5)-18mb/6h, -29mb/6h, -64mb/18h Hugo (1989, 5)-22mb/6h-39mb/12h Opal X 2 (1995, 4)-18mb/6h,-19mb/6h in consecutive times Edouard (1996, 4)-18mb/6h,-27mb/12h Bret (1999, 4)-21mb/6h Keith (2000, )-22mb/6h Iris (2001, 4)-25mb/6h, -38mb/12h Ivan (2004, 5)-22mb/6h,-32mb/12h Katrina (2005, 5)-21mb/6h Rita X 2 (2005, 5)-21mb/6h,-23mb/6h,-58mb/18h Felix X 2 (2007, 5)-18mb/6h,-27mb/6h,-50mb/18h Ike X 2 (2008, 4)-23mb/6h,-21mb/6h, -54mb/18h Igor (2010, 4)-22mb/6h,-39mb/12h, -50mb/18h

Is the Observed Rate of Pressure Fall Likely? Used HURDAT data from to compute 6-h pressure changes for all named storms during mid-August to mid-October Here expressed as 1-h pressure change rates and shown as a function of max. wind speed at time of pressure change 3 hPa/h rates rarely observed Generally happen for systems of hurricane strength

GH Surface Pressures and Winds Surface Pressure Surface Winds Approximate RMW from 18Z P-3 LF radar image Dual-Doppler wind analysis at 0.5 km valid 15Z Pressures and winds appear consistent with strong storm HRD Doppler analysis suggests max winds (in NE eyewall) probably were not sampled by dropsondes

Each of Last 3 Eye Drops Entered Eyewall

9/ UTC 9/ UTC 9/ UTC9/ UTC

9/ UTC9/ UTC9/ UTC 9/ UTC9/ UTC 9/ UTC 9/ UTC9/ UTC9/ UTC

NHC Final MSLP Time Series Compared to P-3 and GH Dropsondes

NOAA P-3 and GH MSLP Measurements Date/TimeP (mb)GPS Alt.TempSLPWind Speed (ms -1 ) Adjusted Psfc (mb)** P3 14/ P3 14/ GH 14/ GH 15/ GH 15/ GH 15/ GH 15/ GH 15/ **Surface pressure adjusted 1 mb for each 10 kt Psfc derived from lowest altitude pressure measurement with GPS altitude, adjusted to surface using corresponding temperature and hypsometric Eq.

NHC Final MSLP Time Series Compared to P-3 and GH Dropsondes