Floyd: (9-16 September 1999)

On 9 September NHC tasked N49RF for a synoptic surveillance mission in Hurricane Floyd east of the Leeward Islands. N49RF took off at 1730 UTC from MacDill AFB and landed in St. Croix at 0230 UTC. The dropsondes should provide excellent documentation of the weakness in the ridge to the NW of Floyd.

GPS dropsonde (HSA) data format

Storm/ Date	Aircraft (Duration)	Altitude	Experiment/ Pattern	Comments (expendables)
Floyd
9 September	N49RF (9 h) GPS dropsondes	45 kft	Synoptic Surveillance Experiment N49RF sampled environmental circulation.	(0 AXBT, 23 GPS sondes)

NHC-tasked a two-aircraft synoptic surveillance mission (N42RF and N43RF) for 11 September 1999 NE of Puerto Rico. Both aircraft departed from MacDill AFB at 1730 UTC. Each aircraft was to release 14 dropsondes along the track with additional eye and eyewall drops possible for during the eye crossing by N43RF. The two aircraft provided important information from flight-level and GPS sonde observations in and around the periphery of Floyd.

Storm/ Date	Aircraft (Duration)	Altitude	Experiment/ Pattern	Comments (expendables)
Floyd
11 September	N42RF (9 h) mission summary (712 Kb) GPS dropsondes One minute listing N43RF (9.2 h) mission summary (76 Kb) GPS dropsondes One minute listing WC-130	14-22 kft 14-22 kft 5 kft	2-Plane Synoptic Surveillance Experiment N43RF sampled environment NW of Floyd, passed through storm center, and returned to Miami. N42RF sampled environment N and NE of storm to within 200 km NW of center, recovering in Bermuda. AFRES recon.	N42RF crossed the frontal boundary 350 nm NW of Floyd, impressive on LF radar; ~800 km long and ~100 km wide. N43RF mission was successful despite instrumentation/data system problems. Sondes worked well and radar composite was transmitted. (0 AXBT, 36 GPS sondes)

Back to index

On 12 September NHC tasked N49RF and N42RF for a 2-plane synoptic surveillance mission. N49RF would depart from MacDill AFB at 1730 UTC and fly to the northeast covering the oceanic areas north and west of Hurricane Floyd, and re turn to Miami. Meanwhile, N42RF, after recovering the night before in Bermuda, would takeoff at 1730 UTC, cover the area northeast of Floyd, fly a figure four pattern through Floyd's center, and land in St. Croix, USVI. The two aircraft surveillance missi on provided important information from both the periphery and inner core regions of an intense hurricane. The flights were conducted a couple of days before a potential landfall in the SE United States, including Florida.

Storm/ Date	Aircraft (Duration)	Altitude	Experiment/ Pattern	Comments (expendables)
Floyd
12 September	N49RF (9 h) GPS dropsondes N42RF (9.2 h) mission summary (2 Mb) GPS dropsondes One minute listing WC-130	45 kft 14-22 kft 10 kft	2-Plane Synoptic Surveillance Experiment N49RF sampled environment N and W of Floyd recovering in Miami. N42RF sampled environment E of Floyd, did figure-4 with 75 nm legs in Floyd's core, and recovered in St. Croix, USVI at 0251 UTC. AFRES recon.	Intense, mature hurricane, surface pressure 936 mb. Eyewall was nearly continuos ring of high reflectivity 50 km across. Moat of low reflectivity outside of eyewall, outer eyewall at 100 km radius. Eye was spectacular, with good visibility of eyewall, sea surface, and sky. Flight-level winds ~135 kts observed in N eyewall. (0 AXBT, 58 GPS sondes)

Back to index

On 13 September NHC tasked N49RF and N42RF for a 2-plane synoptic surveillance mission in Floyd, while N43RF did Extended Cylone Dynamics eXperiment (XCDX) mission with added oceanographic observations. N42RF took off from St. Cr oix, USVI at 1730 UTC and recovered at Tampa International at 0245 UTC. N49RF and N43RF took off from Miami at 1730 UTC and N49RF landed in Savannah, GA at 0230 UTC. N43RF landed in Miami at 0230 UTC changed HRD crews and then ferried to MacDill AFB landi ng at 0345 UTC.

Storm/ Date	Aircraft (Duration)	Altitude	Experiment/ Pattern	Comments (expendables)
Floyd
13 September	N49RF (9 h) GPS dropsondes N42RF (9.2 h) mission summary (1.8 Mb) GPS dropsondes One minute listing N43RF (9.2 h) mission summary (96 Kb) GPS dropsondes AXBT data One minute listing WC-130	45 kft 14-22 kft 12 kft 10 kft	2-Plane Synoptic Surveillance Experiment N49RF and N42RF sampled Floyd environment. N42RF figure-4 with 60 nm legs in Floyd's core. N43RF Extended Cyclone Dynamics Experiment (XCDX) rotating figure-4 with 130 nm legs in Floyd's core. GPS drops on ends of legs, 65 nm from center, and in eyewall on all cardinal directions. Stopped in Miami then recovered at MacDill AFB AFRES recon.	Storm steady state during eyewall replacement after rapid deepening previous day. Storm motion was 11 kt toward 290°. N42RF found eye contracted to 20 km radius compared to 25 km day before. Outer eyewall well formed ring of high reflectivity at ~90 km radius. Max flight-level winds 120 kts, 15 kts lower than previous day. High sonde surface wind failures. Great SFMR and C/Ku-SCAT data should compensate. N43RF collected a unique data set, compromised by equipment problems. LF radar reflectivities low. AVAPS and main data system had failures. (10 AXBT, 76 GPS sondes)

Back to index

On 14 September N49RF synoptic surveillance mission in Floyd with takeoff from Savannah, GA at 1730 UTC and recovering in St. Croix, USVI at 0305 UTC. N43RF was tasked to do a two-plane synoptic surveillance mission with N49RF in to Hurricane Floyd as it passed Nassau, Bahamas with a takeoff from MacDill AFB at 1730 UTC and landing at Tampa International Airport around 0230 UTC.

Storm/ Date	Aircraft (Duration)	Altitude	Experiment/ Pattern	Comments (expendables)
Floyd
14 September	N49RF (9 h) GPS dropsondes N43RF (9.2 h) mission summary (124 Kb) GPS dropsondes One minute listing WC-130	45 kft 14-22 kft 10 kft	2-Plane Synoptic Surveillance Experiment N49RF sample environment of Floyd and Gert. N43RF sample environment S and E of Floyd and figure-4 with 50 nm legs in Floyd's core. GPS drops on ends of legs and in eyewall on cardinal directions. One drop in eye on first pass through center with backup on second pass. Final leg E-W pass N of storm over buoys E of Cape Canaveral, FL. Dropped string of AXBTs to sample SST and MLD in front of storm in region where Dennis passed. Dropped GPS-sonde near buoys and C-MAN sites AFRES recon.	N49RF had some communications problems, but mission successful. N43RF mission had many radar and main data system problems. LF showed Floyd changed considerably from previous night, with completion of eyewall replacement. Large outer eyewall (60 nm diameter) encompassed remains of inner eyewall. Considering problems AOC and HRD crew did great job completing drops for NHC, and getting good wave, surge, and Doppler data on FL coast. (8 AXBT, 54 GPS sondes)

Back to index

On Wednesday 15 September N43RF was tasked to do a single plane XCDX/Air-Sea Interaction experiment into Hurricane Floyd while it passed E of Jacksonville, FL with a takeoff from Tampa International at 1948 UTC recovering back in Tampa.

Storm/ Date	Aircraft (Duration)	Altitude	Experiment/ Pattern	Comments (expendables)
Floyd
15 September	N49RF (9 h) GPS dropsondes N43RF (9.2 h) mission summary (440 Kb) GPS dropsondes AXBT data One minute listing WC-130	45 kft 8 kft 10 kft	Modified Extended Cyclone Dynamics (XCDX)/Air-sea Interaction/Windfields at Landfall Experiment. N49RF Synoptic Surveillance of Hurricane Gert. N43RF did 3 rotated figure-4 with 120 nm legs. AXBT and sonde drops on ends of legs, 60 nm from center, near any C-MAN or buoys, and in eyewall on all cardinal directions. 3 drops in eye on first, fourth, and sixth passes through center. Also two legs along coast NW of storm for storm surge mapping and to drop sondes in offshore flow and near 3 instrumented towers and DOW. AFRES recon.	LF radar showed eye very large (60-70 nm diameter) with strong reflectivities >200 nm N of center. S eyewall reflectivity fairly weak, but still closed. Major band extended 100-160 nm E from center. Sondes nearly flawless, providing great mapping of vortex. AXBTs very good, with 17/22 providing SST and MLD as storm interacted with Gulf Stream. TA radar on coastal legs great for comparison with 2 WSR-88Ds and DOW. Great SRA wave data. AOC crew practiced flying SRA along coastline in dark and heavy rain. (22 AXBT, 62 GPS sondes)

Back to index

On Thursday 16 September N42RF scheduled for Windfields at Landfall mission with take off time 0300 UTC. At briefing time, the pilots expressed concern about operating over land where mesovortex signatures had earlier been report ed north of Floyd. Therefore, over land portion of the flight plan was eliminated. The remaining portions of the landfall experiment included an initial "figure 4", a series of coastal legs and a box pattern.

Storm/ Date	Aircraft (Duration)	Altitude	Experiment/ Pattern	Comments (expendables)
Floyd
16 September	N42RF (9.2 h) mission summary (568 Kb) GPS dropsondes AXBT data One minute listing WC-130	8 kft 10 kft	Windfields at Landfall Experiment N42RF 100 nm legs with GPS drops at C-MAN sites, buoys, and portable towers and mesonets from OU and TTU, on ends of legs, and in eyewall. Flight legs had radials off KLTX, KMHX, and the DOW. AXBT deployments were made along Gulf Stream. AFRES recon.	Eye located offshore for first 2 penetrations. Completed modified "figure 4" and coastal legs before center landed. N42RF Flight-level data plus N43RF SFMR in surface wind analysis at 0700 UTC PBL from sondes good near coast and C-MAN. Excellent data set for analysis of flight-level winds from N42RF, AFRES, and sondes. Near surface winds available from sondes, SFMR, and C/Ku-SCAT to document offshore and onshore flow. TTU, NSSL, and OU deployed three 10 m towers, three mobile mesonets, and DOW. Mobile mesonets gathered obs in Floyd's eye and eyewall. (9 AXBT, 29 GPS sondes)

Back to index

Updated Wednesday, 24 November 1999