Dennis: (25-31 August 1999)

On Tuesday 24 August NHC tasked N49RF and N42RF for a 2-plane synoptic surveillance mission in Tropical Storms (TS) Dennis and Emily on Wednesday 25 August. Both aircraft took off at 1730 UTC, 25 August and landed in Miami at 0230 UTC. The N42RF and N49RF dropsondes should provide excellent documentation of the weakness in the ridge to the N of Dennis, and the N49RF drops should provide some upper air information around Emily. The surprising observation was the near stationarity of both storms relative to their previous fixes 6-12 h prior to these flights.

GPS dropsonde (HSA) data format

Storm/ Date	Aircraft (Duration)	Altitude	Experiment/ Pattern	Comments (expendables)
Dennis
25 August	N49RF (9 h) GPS dropsondes N42RF (9.2 h) mission summary (24 Kb) GPS dropsondes AXBT data One minute listing WC-130	45 kft 14-22 kft 1500 ft	2-Plane Synoptic Surveillance Experiment N49RF sampled Emily, then N between Cindy and Dennis to point N of front off the E coast US dropping 22 sondes, and recovered in Miami. N42RF sampled W of Bahamas SW of TS Dennis, figure-4 with 55 nm legs in Dennis' core, then sampled S, E, and N of storm, dropping AXBTs across its potential track.. AFRES recon.	N49RF passed near Emily, little convection except S of center. Found low-level center visually. Passed through front at 33.5°N, 69°W and 75°W. N42RF found Dennis 1° E than expected. Large band of convection S and SE of center. No deep convection W and NW of center. 55 nm E was a large stratiform area and 55 nm S was middle of band. Track skirted S of anvil then E edge of stratiform region 100 nm E of center. Track passed through ridge axis around 27° and 70 nm S of front. (6 AXBT, 44 GPS sondes)

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On Thursday 26 August all three NOAA aircraft were tasked by NHC for a 3-plane synoptic surveillance of Hurricanes Cindy and Dennis and TS Emily taking off from Miami at 1730 UTC. N49RF would depart Miami and sample the environme nt around Emily and S of Cindy, recovering in St. Croix, USVI. N43RF would make a coordinated penetration of Dennis together with N42RF to get true dual-Doppler radar coverage, and then continue E to make a penetration through Cindy and then sample the en vironment N of Cindy recovering in Bermuda. N43RF would sample the environment N of Dennis up to 35°N and recover in Bermuda. At briefing time N49RF had a flat tire and a spare wouldn't be available until 5 PM. So upon consultation with NHC strategy c hanged to focus on Dennis, with N42RF altering its track to sample Dennis with a series of figure-4s in the storm core, followed by a sampling of the environment S and E of the storm recovering in Bermuda. N43RF encountered air traffic problems N of the s torm in the location of the ridge axis and had to shorten the pattern, leaving a hole in the sampling. Despite the lack of N49RF and the air traffic control problems the data set should help define the environment surrounding Dennis.

Storm/ Date	Aircraft (Duration)	Altitude	Experiment/ Pattern	Comments (expendables)
Dennis
26 August	N42RF (9 h) mission summary (24 Kb) GPS dropsondes AXBT data One minute listing N43RF (9.2 h) mission summary (80 Kb) GPS dropsondes AXBT data One minute listing WC-130	12-22 kft 14-22 kft 5000 ft	2-Plane Synoptic Surveillance Experiment Both aircraft coordinated 75 nm radius leg in core and N42RF finishing rotating Fig. 4. N43RF sampled environment N of Dennis up to 35°N recovering in Bermuda. N42RF sampled environment S and E of storm recovering in Bermuda. AFRES recon.	Coordinated dual-Doppler leg went well, Dennis S of forecast track. Eye getting organized with radius of 20 nm. Eyewall wavenumber 2 asymmetry major axis rotated CCW ~90°/ 1 h. Major band SE of center, W side eyewall open at low altitude and virga from anvil aloft. Sondes and AXBTs 50 nm NW, SE, NE, and SW of center. 3 eyewall drops SE, NE, and NW of center, and 2 eye drops. Drop at flight level center landed E of surface center with 997 mb, 2nd drop at surface center had 993 mb. SST N of center >29°C, SE of center 28°C. (7 AXBT, 39 GPS sondes)

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On Friday 27 August N43RF was tasked to do a single plane XCDX/Air-Sea Interaction experiment into Hurricane Dennis while it passed just E of Nassau, Bahamas with a takeoff from Bermuda at 1730 UTC and recovery in Miami at 0230 U TC. N49RF tasked to do a synoptic surveillance mission to sample the environmental circulation surrounding Dennis with a takeoff from Miami, FL at 1730 UTC and recovery in Bermuda.

Storm/ Date	Aircraft (Duration)	Altitude	Experiment/ Pattern	Comments (expendables)
Dennis
27 August	N49RF (9 h) GPS dropsondes N43RF (9.2 h) mission summary (76 Kb) GPS dropsondes AXBT data One minute listing WC-130	45 kft 14 kft 5000 ft	2-Plane Synoptic Surveillance Experiment. N49RF sampled environmental circulation dropping 24 sondes. N43RF 150 nm radius rotating Fig. 4 in core. GPS drops on ends of legs, 75 nm from center, and in eyewall on all cardinal directions. Two drops in eye on first and last pass and at C-MAN or buoy locations. AFRES recon.	Dennis had well-defined eye with strongest convection N and W eyewall Late in flight, active convection in SE bands with frequent lightning. AXBTs launched with sondes at 75 nmi radius E, NE, N and NW of center, and in eyewall of each leg 1 SFMR frequency bad and error checking routine not operating properly ( 8 AXBT, 58 GPS sondes)

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On Saturday 28 August N42RF was tasked to do a single plane XCDX/Air-Sea Interaction experiment into Hurricane Dennis while it passed just NE of Abaco, Bahamas and just E of FL with a takeoff from Bermuda at 1730 UTC recovering a t MacDill AFB. N49RF was tasked to do a synoptic surveillance mission to sample the environmental circulation surrounding Dennis with a takeoff from Bermuda at 1730 UTC and recovering in MacDill AFB in Tampa.

Storm/ Date	Aircraft (Duration)	Altitude	Experiment/ Pattern	Comments (expendables)
Dennis
28 August	N49RF (9 h) GPS dropsondes N42RF (9.2 h) mission summary (156 Kb) GPS dropsondes AXBT data One minute listing WC-130	45 kft 14 kft 10 kft	Modified Extended Cyclone Dynamics (XCDX)/Air-sea Interaction Experiment. N49RF Synoptic Surveillance sampled environmental circulation dropping 28 sondes. N42RF 150 nm radius rotating Fig. 4 in core. GPS drops on ends of legs, 75 nm from center, and in eyewall on all cardinal directions. Two drops in eye on first and last pass and at C-MAN or buoy locations. AFRES recon.	Dennis slowly intensifying category 2 (969-970 mb) with ~50 nm eye. Storm had just undergone eyewall replacement E-W penetration had peak MBL wind of 93 kt and 10-m wind of 76 kt in the E and W eyewall. good sonde coverage to 150 nm from center. dropped sondes at buoy 41010 and CMAN SPGF1. AXBTs (only 50% worked) provided SST and MLD observations N of storm in vicinity of D'Asaro's floats (6 AXBT, 58 GPS sondes)

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On Sunday 29 August N43RF was tasked to do a single plane XCDX/Air-Sea Interaction experiment into Hurricane Dennis while it passed just E of Jacksonville, FL with a takeoff from MacDill AFB at 1730 UTC recovering back in Tampa. N49RF was tasked to do a synoptic surveillance mission to sample the environmental circulation surrounding Dennis with a takeoff from MacDill, AFB at 1730 UTC and recovering in Providence, RI.

Storm/ Date	Aircraft (Duration)	Altitude	Experiment/ Pattern	Comments (expendables)
Dennis
29 August	N49RF (9 h) GPS dropsondes N43RF (9.2 h) mission summary (148 Kb) GPS dropsondes AXBT data One minute listing WC-130	45 kft 14 kft 10 kft	Modified Extended Cyclone Dynamics (XCDX)/Air-sea Interaction Experiment. N49RF Synoptic Surveillance sampled environmental circulation dropping 28 sondes. N43RF 120 nm radius rotating Fig. 4 in core. GPS drops on ends of legs, 75 nm from center, and in eyewall on all cardinal directions. Two drops in eye on first and fourth (last) pass and at C-MAN or buoy locations. AFRES recon.	Landmark mission providing first successful transmission and use of SFMR surface winds SFMR used by hurricane specialists and in HRD surface wind analyses for the first time. Dennis almost category 3 (963 mb) with a ~50 nm eye and large stratiform area to NW of the center. Peak MBL winds of 95 kt and 10-m winds of 90 kt. dropped sondes at buoys 41004, 41010 and CMAN FBIS1, FPSN7 AXBTs provided ocean thermal structure along E edge of Gulf Stream. (21 AXBT,58 GPS sondes)

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On Monday 30 August N42RF was tasked to do a Windfields at Landfall experiment into Hurricane Dennis while it passed over eastern NC with a takeoff from MacDill at 1730 UTC recovering at MacDill AFB. N49RF was tasked to do a syno ptic surveillance mission to sample the environmental circulation surrounding Dennis with a takeoff from Providence, RI at 1730 UTC and recovering in MacDill, AFB. The aircraft returned to MacDill by 2130 UTC.

Storm/ Date	Aircraft (Duration)	Altitude	Experiment/ Pattern	Comments (expendables)
Dennis
30 August	N49RF (9 h) GPS dropsondes N42RF (9.2 h) mission summary (148 Kb) One minute listing WC-130	45 kft 14 kft 10 kft	Windfields at Landfall Experiment. N49RF Synoptic Surveillance sampled environmental circulation dropping 22 sondes. N42RF 100 nm legs with GPS drops at C-MAN sites, buoys, and portable towers from Clemson and TTU, on ends of legs, and in eyewall. AFRES recon.	N42RF aborted near Cape Fear, NC before pattern began because of hydaulic fluid leak. (0 AXBT,22 GPS sondes)

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Updated Monday, 22 November 1999