the controversy regarding hs3 surface pressure observations during the rapid intensification of...
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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 measurementTRANSCRIPT
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The Controversy Regarding HS3 Surface Pressure Observations
During The Rapid Intensification of Edouard on September 14-15
Scott BraunNASA/GSFC
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Controversy over Dropsonde Data During Sept. 14-15 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
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NOAA P-3 and GH MSLP Measurements
Date/Time Location relative to
center
Psfc (mb)
Wind Speed (kt)
Estimated MSLP(mb)**
P3 14/1500 Eye center 983 4 983
P3 14/1707 NE 984 80 976
GH 14/2103 N 972 89 963
GH 15/0031 N 967 86 958
GH 15/0034 S 977 56 971
GH 15/0217 W_SW 975 56 970
GH 15/0428 N 971 84 963
GH 15/0552 NW 972 68 965
**Surface pressure adjusted 1 mb for each 10 kt
Adjusted Psfc derived from lowest altitude pressure measurement
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GH Surface Pressures and Winds
Surface Pressure Surface Winds
Pressures and winds appear consistent with strong storm
Wind barbs show storm-relative winds
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NHC Final MSLP Time Series
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NHC Final MSLP Time SeriesP-3 drops
North-sideGH drops
South-sideGH drops North-side
GH drops
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The Beginning of a Convective Burst
9/14 1045 UTC 9/14 1145 UTC
9/14 1345 UTC9/14 1245 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
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The First P-3 Drop
9/14 1445 UTC
9/14 1457 UTC
9/14 1500 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
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Gradual Formation of a New Eye
9/14 1515 UTC 9/14 1545 UTC
9/14 1615 UTC 9/14 1645 UTC
• CB cloud shield continues to circle around southern to eastern sides
• New eye begins to for by ~1645 UTC
9/14 1618 UTC
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Last P-3 Drop
9/14 1715 UTC
9/14 1707 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
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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.
9/14 2115 UTC
1st GH “Eye” Drop
700800
1000
600500
400
300
200
100
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2nd GH Eye DropGH 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.
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2nd GH Eye DropGH 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.
700800
1000
600500
400
300
200
100
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Edouard Appears to Undergo an ERC
9/15 0215 UTC 9/15 0415 UTC 9/15 0545 UTC
9/15 0815 UTC 9/15 1315 UTC9/15 0645 UTC
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Storm Evolution and Intensity Change
CB beginsSmall eye forms
Small eye begins breakdown
Large eye begins to form
>3 hPa/h pressure fall
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Is the Observed Rate of Pressure Fall Likely?
• Used HURDAT data from 1970-2013 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
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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)
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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)
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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?
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Extra slides
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15 Past Storms With DP/DT≤3mb/h• Anita (1977, 5) -18mb/6h, -32mb/12h in consecutive times• Gloria (1985, 4) -24mb/6h second 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
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Is the Observed Rate of Pressure Fall Likely?
• Used HURDAT data from 1970-2013 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
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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
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Each of Last 3 Eye Drops Entered Eyewall
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9/15 0041 UTC 9/15 0532 UTC
9/15 0949 UTC 9/15 1520 UTC
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9/14 1126 UTC 9/14 1813 UTC 9/14 2119 UTC
9/15 0949 UTC 9/15 1158 UTC 9/15 1520 UTC
9/15 0041 UTC 9/15 0532 UTC 9/15 0641 UTC
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NHC Final MSLP Time Series Compared to P-3 and GH Dropsondes
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NOAA P-3 and GH MSLP Measurements
Date/Time P (mb) GPS Alt. Temp SLP Wind Speed (ms-1)
Adjusted Psfc (mb)**
P3 14/1500 983 4 983
P3 14/1707 984 80 976
GH 14/2103 970 33.23 299.24 974 89 965
GH 15/0031 966 30.00 299.54 970 86 961
GH 15/0034 975 30.60 299.45 979 56 973
GH 15/0217 974 30.80 298.89 978 56 972
GH 15/0428 970 31.10 299.42 973 84 965
GH 15/0552 971 31.40 299.30 974 68 967
**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.
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NHC Final MSLP Time Series Compared to P-3 and GH Dropsondes