I don’t get it

June 13, 2006

The 11 PM Advisory for Alberto set maximum sustained winds at 70 mph. The justification in the discussion was

AN AIR FORCE RESERVE RECONNAISSANCE AIRCRAFT MEASURED 68-KT WINDS AT 700 MB IN THE NORTHEAST QUADRANT JUST NORTHWEST OF CEDAR KEY FLORDIA…

Now here is the raw observation (the boldfaced ob is the one cited in the discussion).

000

SXXX50 KNHC 130124
AF307 0501A ALBERTO HDOB 15 KNHC
0117 2913N 08340W 03049 0099 192 038 064 064 039 03193 0000000000
0117. 2914N 08339W 03048 0098 191 041 076 076 042 03191 0000000000
0118 2916N 08337W 03050 0097 190 044 078 078 045 03191 0000000000
0118. 2918N 08336W 03048 0093 186 043 078 078 045 03186 0000000000
0119 2919N 08335W 03047 0090 181 050 070 070 051 03182 0000000000
0119. 2921N 08333W 03044 0085 184 061 066 066 063 03174 0000000000
0120 2923N 08332W 03054 0088 179 059 060 060 061 03187 0000000000
0120. 2925N 08331W 03044 0086 179 066 062 062 066 03175 0000000000
0121 2927N 08329W 03046 0088 176 067 064 064 068 03179 0000000000
0121. 2928N 08327W 03050 0090 178 064 068 068 066 03185 0000000000
0122 2930N 08326W 03052 0090 182 056 074 074 058 03187 0000000000
0122. 2932N 08325W 03047 0091 176 060 068 068 062 03183 0000000000
0123 2933N 08327W 03049 0096 173 058 062 062 060 03191 0000000000
0123. 2932N 08329W 03043 0094 182 055 070 070 057 03182 0000000000
0124 2931N 08330W 03049 0093 175 058 062 062 061 03187 0000000000
0124. 2930N 08331W 03050 0093 174 061 066 066 063 03188 0000000000
0125 2929N 08331W 02938 0086 178 059 076 076 059 03068 0000000000
0125. 2928N 08331W 02770 0074 178 059 082 082 061 02888 0000000000
0126 2927N 08332W 02599 0062 173 059 086 086 062 02705 0000000000
0126. 2925N 08333W 02436 0052 165 053 088 088 057 02532 0000000000

That just happens to be near observation station KTNF1. In that set of obs we see

The station is located at 2949N 8335W. In this set of obs there is one from position 2933N 08327W, 18 miles SSE of the observation. That ob from the hurricane hunter, (which is italicized), showed 60 knots (at the 700 millibar level, roughly 10000 feet). The station at the surface, however, recorded less than 20 knots during that time period.

This flight level winds are not showing up at the surface. Another example of this shows up in a dropsonde ob taken shortly later.

000 UZNT13 KNHC 130152
XXAA 63019 99295 70835 08193 99008 22001 05027 00068 20805 05533
92741 18605 10050 85466 16003 70105 08200 88999 77999
31313 09608 80124
61616 AF307 0501A ALBERTO OB 08

Dropsonde observation from 2930N 8330W indicated 50 knots at the 925 millibar level, but only 27 knots at the surface. The standard rule of thumb would call for 40-45 knots.

It is evident that the rules of thumb for the relationship between flight level and surface winds are not holding at this time, so I don’t understand why the NHC advisory is using them.

Highest ob I’ve seen by the way, is SGF01, which is located southeast of Panama City. They were reporting 30 knot winds at 04Z. Tallahassee just reported winds of a similar magnitude.

LATER AS ALBERTO IS COMING ASHORE:

Peak wind observations from various stations around the coast (subtract 4 hours for EDT) 

Appalachicola 29 knots 0724Z

Tallahassee 36 knots 0505Z

Cross City 26 knots 1348Z

Tampa 39 knots 0707Z

Venice 38 knots 0639Z

Highest guest I’ve seen in the buoy observations was 42.7 knots at buoy 42036. KTNF1 is at the same place Alberto is making landfall (Keaton Beach), and the highest gust reported there was 29 knots at 1400Z.

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