Effects of Synoptic Surveillance on model forecasts for
21 August 1999 1800 UTC
BRET.

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

TRACK AND INTENSITY PERFORMANCE
TRACK (km)
MODEL	12 h	24 h	36 h	48 h	60 h	72 h	84 h	96 h	108 h	120 h

AVNN	24.	64.	80.	119.	223.	318.
AVAL	15.	46.	60.	140.	254.	338.
%IMP	38%	28%	25%	-18%	-14%	-6%

GFNO	56.	89.	60.	30.	102.	223.
GFAL	44.	68.	39.	59.	94.	192.
%IMP	21%	24%	35%	-97%	8%	14%
INTENSITY (kt)
MODEL	12 h	24 h	36 h	48 h	60 h	72 h	84 h	96 h	108 h	120 h

AVNN	-93.	-84.	-50.	-5.	-4.	-6.
AVAL	-95.	-86.	-50.	-7.	-2.	-6.
%IMP	-2%	-2%	0%	-20%	50%	0%

GFNO	-46.	-26.	6.	14.	28.	12.
GFAL	-43.	-26.	-2.	14.	25.	13.
%IMP	7%	0%	67%	0%	11%	-8%

SHNO	-29.	-18.	25.	73.	77.	84.
SHAL	-29.	-18.	25.	73.	77.	82.
%IMP	0%	0%	0%	0%	0%	2%

DSNO	-29.	-18.	-12.	5.	1.	3.
DSAL	-29.	-18.	-12.	5.	1.	3.
%IMP	0%	0%	0%	0%	0%	0%

Landfall forecasts
23/0000UTC 26.9N 97.4W Central Padre Island, TX 30 h into forecast
LAT	LON	FTIME	ERROR	LOCATION
AVNN	26.92	97.39	40.5	2.4 Central Padre Island, TX
AVAL	26.69	97.34	35.0	24.1 Central Padre Island, TX
%IMP		52%	-904%
LAT	LON	FTIME	ERROR	LOCATION
GFNO	26.93	97.36	36.5	5.2 Central Padre Island, TX
GFAL	26.55	97.31	32.5	39.9 Port Mansfield, TX
%IMP		62%	-667%

Figure 1. NCEP 850 - 200 hPa mean wind analysis for 21 August 1999 1800 UTC (Hurricane Bret).

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 21 August 1999 1800 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 21 August 1999 1800 UTC.

Figure 4. 12-h forecast differences in the 850 - 200 hPa mean wind between the no and all dropwindsonde cases for 21 August 1999 1800 UTC.