Effects of Synoptic Surveillance on model forecasts for
25 August 1999 1200 UTC
DENNIS.


QuickTime movie of DLM wind model forecasts
QuickTime movie of DLM wind data increments


TRACK AND INTENSITY PERFORMANCE

TRACK (km)
MODEL12 h24 h36 h48 h60 h72 h84 h96 h108 h120 h
AVNN75.114.89.78.111.100.126.173.196.322.
AVAL90.108.102.83.104.102.156.201.179.289.
%IMP-20%5%-15%-6%6%-2%-24%-16%9%10%
GFNO130.157.228.306.466.747.1163.1717.
GFAL97.110.127.136.279.411.694.1051.
%IMP25%30%45%56%40%45%40%39%
INTENSITY (kt)
MODEL12 h24 h36 h48 h60 h72 h84 h96 h108 h120 h
AVNN-36.-38.-38.-33.-41.-51.-55.-52.-52.-47.
AVAL-32.-35.-36.-33.-41.-52.-56.-54.-56.-50.
%IMP11%8%5%0%0%-2%-2%-4%-8%-6%
GFNO-13.-1.0.22.13.17.14.-9.
GFAL-4.13.11.25.16.16.16.1.
%IMP69%-1200%und%-14%-23%6%-14%89%
SHNO-15.-13.-5.2.2.-9.-13.-14.-15.-12.
SHAL-15.-12.-5.2.3.-9.-12.-13.-14.-11.
%IMP0%8%0%0%-50%0%8%7%7%8%
DSNO-15.-13.-5.2.2.-9.-13.-14.-15.-12.
DSAL-15.-12.-5.2.3.-9.-12.-13.-14.-11.
%IMP0%8%0%0%-50%0%8%7%7%8%

Landfall forecasts

28/0700UTC 26.6N 76.8W Abaco Islands, Bahamas 67 h into forecast
MODELLATLONTIMEERRORLOCATION
AVNN24.6274.0120.02355.7 Near Cockburn Town, San Salvador, Bahama Islands
AVAL26.9076.4258.550.3 Near Hope Town, Abaco Island, Bahama Islands
%IMP82%86%
GFNO24.5074.1917.52350.5 Near Cockburn Town, San Salvador, Bahama Islands
GFAL24.3274.3321.02356.0 Cockburn Town, San Salvador, Bahama Islands
%IMP7%-2%
04/2100UTC 34.8N 76.5W Cape Lookout National Seashore, NC 249 h into forecast
MODELLATLONTIMEERRORLOCATION
AVNN235.1575.83116.072.3 Ocracoke, NC
AVAL234.9876.27116.029.0 Lupton, NC
%IMP0%60%
GFNO41.1269.8392.0913.4 Surfside, Nantucket, MA
GFAL235.1075.9386.061.7 Ocracoke, NC
%IMP-4%93%

Figure 1. NCEP 850 - 200 hPa mean wind analysis for 25 August 1999 1200 UTC (Tropical Storm Dennis).

Figure 2. Track forecasts for the no dropwindsonde (NO or NN) and the all dropwindsonde (AL) runs for the AVN and GFDL models initialized on 25 August 1999 1200 UTC. The best track is shown in black.

Figure 3. Initial condition differences in the 850 - 200 hPa mean wind between the no and all dropwindsonde cases for 25 August 1999 1200 UTC.

Figure 4. 12-h forecast differences in the 850 - 200 hPa mean wind between the no and all dropwindsonde cases for 25 August 1999 1200 UTC.

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