Bret: (20-22 August 1999)

Friday morning (20 August) brought TS Bret (named the evening before). We planned a single WP-3D (N43RF) mission to study the intensity change, as well as, to check out the new algorithm to generate surface wind and rain estimates using the Stepped Frequency Microwave Radiometer (SFMR). The new algorithm would provide NHC with an independent estimate of the surface wind speed to compare with reductions from flight level winds and GPS-sondes. The flight, in and out of AOC (MacDill AFB in Tampa) departed at 1730 UTC and recovered at 0208 UTC. AXBTs were also dropped across the warm ring sampled in late July.

GPS dropsonde (HSA) data format

Storm/ Date	Aircraft (Duration)	Altitude	Experiment/ Pattern	Comments (expendables)
Bret
20 August	N43RF (9.2 h) mission summary(868 Kb) GPS dropsondes AXBT data One minute listing WC-130	14 kft 1500 ft	Modified Extended Cyclone Dynamics (XCDX)/Air-sea Interaction Expeiment. 75 nm radius rotating Fig. 4 in core, followed by E-W leg along 24° N dropping AXBTs. AFRES recon.	Bret became hurricane. Documented beginning of eyewall formation Numerous AXBT and GPS-sonde drops in inner core. Relatively deep (>50 m) mixed layer depth (MLD) and >29° C SST. Strongest GPS sonde winds were 62 kt. Aircraft was struck by lightning twice. (22 AXBT, 19 GPS sondes)

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On 20 August we planned a second modified (XCDX) mission for N42RF on Saturday (21 August) to continue monitoring intensification while the G-IV (N49RF) did a synoptic surveillance mission. Also started making plans for possible landfall missions, moving more AXBTs and people to AOC on Saturday. As part of the preparations we contacted the landfall teams from Texas Tech University (TTU), University of Oklahoma, University of Alabama Huntsville, and Clemson University to see if th ey wanted to position there portable towers, profiler, or Doppler on Wheels in TX ahead of Bret. Only the two towers from TTU were available. Saturday morning (21 August) the cold core low had moved over TX and Hurricane Bret was tracking N along 95° W. N49RF and N42RF missions were scheduled to depart AOC at 1730 UTC. The combination of a N49RF surveillance and the N42RF inner core flight should provide a great data set of rapid intensification.

Storm/ Date	Aircraft (Duration)	Altitude	Experiment/ Pattern	Comments (expendables)
Bret
21 August	N49RF (9 h) GPS dropsondes N42RF (9.2 h) mission summary (688 Kb) GPS dropsondes AXBT data One minute listing WC-130	45 kft 14 kft 5000 ft	Modified Extended Cyclone Dynamics (XCDX)/Air-sea Interaction Expeiment. 75 nm radius rotating Fig. 4 in core, with E-W leg along 26° N to drop AXBTs across storm track, warm ring sampled in July, and near west- and mid-Gulf buoys. AFRES recon.	N49RF documented upper-level ridge just N of Yucatan, which with cold low over TX drove Bret N. Bret deepened >25 mb during the day. Bret cat 4 storm, thus seeing storm go from cat 1 to 4 in <24 h. Sondes had eyewall winds >125 kts below WP-3D flight level with 950 mb pressure. 1 sonde had MBL wind 141 kt and 155 kt wind at 900 m while flight level winds were 110 kt. Made first combined Ku/C-SCAT measurements in intense TC. AXBTs documented SST and MLD structure. (18 AXBT, 55 GPS sondes)

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On 21 August we planned for landfall missions the next day, tentatively near Brownsville TX. Two flights were schedued: (1) N43RF for 1730 UTC Sunday (22 August) to cover the earliest possible landfall; and (2) N42RF for 0200 UTC Monday (23 August) to cover the latest possible landfall. We assisted the TTU crews pick sites near Brownsville and Corpus Christi, TX; one tower near Corpus Christi WSR-88D and the other at Kingsville Auxiliary Naval Air Station, about 40 km SW of Corpu s Christi (with help from CARCAH and the FEMA liaison team at NHC). Sunday morning (22 August) it was apparent landfall would happen between Brownsville and Corpus Christi around 0000 UTC 23 August. We canceled the N42RF flight. N43RF took off at 1730 UTC and arrived at the storm around 2015 UTC while the center was 10 nm off Padre Island. The combination of the Doppler radar, GP-sondes, and SRA storm surge is going to make an excellent landfall data set.

Storm/ Date	Aircraft (Duration)	Altitude	Experiment/ Pattern	Comments (expendables)
Bret
22 August	N43RF (9.2 h) mission summary (328 Kb) GPS dropsondes AXBT data One minute listing WC-130	14 kft 5000 ft	Windfields at Landfall Expeiment. 75 km leg Figure-4 through center at 12 kft, penetrating 10-15 km over land. S-N run was along barrier island to map storm surge AFRES recon.	GPS-sonde drops in high wind region of storm, both onshore and offshore flow documenting wind field changes at landfall. Radials off Brownsville and Corpus Christi WSR-88D radars. NASA/GSFC Scanning Radar Altimeter (SRA) mapped surge along Padre Island. Surface wind field mapped with SFMR. (9 AXBT, 35 GPS sondes)

Overall, the Bret flights were a great success. We captured an excellent data set in a rapidly intensifying TC over 3 days which should provide excellent documentation of the intensity changes in the inner core, as well as some good data on the envir onment around the storm on 21 August. The landfall experiment provided a further increase to our knowledge about the wind field evolution near landfall. Bret was the most intense storm we have sampled in our 5 years of doing the landfall experiments. The strengths of this landfall data set will be the excellent WSR-88D coverage (possibly providing some dual-Doppler observations), the GPS-sondes in the onshore and offshore flow within the eyewall, and the SRA surge observations along Padre Island. The TTU towers should provide some observations of the wind field evolution after landfall.

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Updated Monday, 22 November 1999