Winds at Landfall Experiment
(950801I Aircraft 43RF -- single aircraft)
|Chief Scientist ||J. Gamache
|Doppler Scientist ||M. Black
|Cloud Physics Scientist ||R. Black
This document is divided into 3 sections (Each section is written by the Chief Scientist):
By the afternoon of 31 July 1995, it was apparent that the South Florida Coast was likely to be struck by Hurricane Erin, a minimal hurricane. Thus, J. Gamache, R. Black, and M. Black deployed to Tampa to be ready to fly in Hurricane Erin during the dayt
ime on 1 August 1995. Originally take off was set for early morning (1200 UTC), but by the time we retired, the departure had been moved to late morning. Once the clock starts to run, there are officially 15 hours to complete the flight. It became appa
rent that Hurricane Erin was not going to strike as early, or be as intense, probably because of an interaction with an upper-level low immediately in front of it. Take off time was moved to as late a time as possible to still allow a 9-hour flight and s
tay within the crew rest requirements, and therefore a 1900 UTC take off was finally chosen. Hurricane Erin also was threatening to pass near Tampa, so the aircraft was not expecting to return home, but rather to land in Key West.
There are several mission modules associated with the Windfields at Landfall Experiment, but no specific order is set, except for an initial figure "4" reconnaissance. If the aircraft is within about 100 nm of a NEXRAD Doppler radar, the aircraft will at
tempt to fly along radials between the storm center and the radar, but when the storm is farther out, figure "4" pattern may be flown to document the structure and evolution of the hurricane inner core. Overflights of buoys or C-MAN stations may also be
done to improve the extrapolation of flight-level winds to the surface. The order and length of flight modules will be dictated by circumstances. Flight 950801I1 would begin with "4" patterns, since the storm was still farther from the shore than desir
ed, attempt to overfly buoys, and near the end of the flight, fly the radials between radar and storm center to provide airborne-ground-based dual Doppler observations. Flight level for 950801I1 was set to 10,000 ft.
N43RF took off from Tampa, FL, at 1909 UTC. Flight time to the IP was slightly less than 1 h. The aircraft began its descent to 10,000 ft at 1959 UTC, and reached the IP of 26.5N 78.6W at 2004 UTC. From there it began the first "4" pattern, heading E t
hrough the storm center. To insure the best quality Doppler wind field, the aircraft did not deviate more than 10-20 degrees, and since the center at flight level was poorly known, beforehand the closest point of approach (CPA) was estimated to be 5 nm N
of the storm center. The estimated storm center at 2011 UTC was 26.5N 78.04W, or about 120 nm east of the Florida coast, and just S of Palm Beach. The USAF made a 5,000 ft fix at 2001 UTC (26.4, 77.8W), and they estimated the minimum surface pressure t
o be 980 mb. N43RF found 50 kt winds to the W of the center, and 70 kts to the E of the center. N43RF maintained the same track out to 26.54, 77.1W, where it then turned to track 315 on the downwind leg of the "4". A maximum windspeed recorded on this
downwind leg was 78 kts, basically along the flight track. At 2040 UTC, when the aircraft was at 27.47N 78.12 W, it turned S and began the second flight leg through the storm center. N of the center a peak wind of 80 kts was observed near 27.23N 78.17 W,
and S of the center the peak wind was 42 kts. We estimated the center to be at 26.52N 78.15W at 2054 UTC. At the end of the leg (2107 UTC, 25.64N 79.15W), N43RF tracked 45 degrees downwind relative to storm center to begin a second figure "4" that was
rotated 45 degrees from the first. Due to a mixup no center was found during this third pass through the center. This leg was extended
outward from the center to 27.14N, 79.00W (at 2141 UTC) to facilitate a buoy flyover. At this turning point the winds were measured to be 52 kts from 56 degrees heading. N43RF then turned south, and the buoy flyover at 26.67N, 79.00W occurred at 214657
UTC, and the winds measured at 10,000 ft were 58 kts from 28 degrees. The flight continued S to 26.33N 79.00W (c. 2155), when we turned to track 45 degrees back through the storm center. The CPA to the center was at 26.50N 78.25W, time 2209 UTC, and the
minimum central pressure extrapolated from 10,000 ft was 982 mb.
The track continued NE to 27.05N 77.67W, when the aircraft turned W to line up on a radial with the Melbourne WSR-88D. At 2235 UTC the aircraft was at 27.12N 79.17W and it began its radial toward Melbourne. The wind at this site was 44 kts from 56 degre
es. The aircraft continued along this track until no more appreciable echo was seen on the airborne Doppler radar. It then turned back toward the storm center to begin another "4" pattern. The center was found at time 225845 UTC location 26.76N 78.54W,
and the minimum surface pressure was extrapolated to be 979 mb. The aircraft continued southeastward until 2310 UTC, when it reached 26.24N 77.77W, where the winds were 46 kts from 195 degrees. The downwind leg was on a N heading, ending at 27.47N 77.7
7W (2325 UTC). The winds there were 63 kts from 140 degrees. The aircraft tracking along 235 degrees, finding a maximum wind on the NE side of 86 kts from 146 degrees (27.17N 78.24N). The CPA to the center on this approach was about 3 nm, and was estim
ated to be 26.78N 78.70W. N43RF continued southwestward to 26.84N 78.72W (c. 2354 UTC), and then turned toward 190 degrees to set up for a radial outward from the Miami WSR-88D along a southern rainband. The radial along the rainband went from 25.57N 79
.54W (0002 UTC) to 25.50N 78.85W (0011 UTC). The aircraft then turned N and went to the storm center. The center was found to be near 27.00N 28.87W (0032 UTC).
The aircraft then flew another radial toward the Melbourne WSR-88D, reaching its CPA at 0054 UTC (27.94N 80.27W). The pattern was then flown out from the radar so that the aircraft would overfly a CMAN station. This was nearly a southern track and was j
ust off the Florida coastline. The actual CMAN overflight occurred at 0113 UTC (26.60N 80.04W). The aircraft measured a wind of 36 kts from 352 degrees. The aircraft then tracked back to the center finding it at 0127 UTC (27.14N 79.19W), where it extra
polated the minimum pressure to be 981 mb. We then set up for next radial between the storm center and the Melbourne radar, reaching our closest approach of the day to the Melbourne radar at 0138 UTC (27.58N 79.88W). N43RF then did a 180 degree turn an
d heading one more time to the storm center, arriving there at 0150 UTC (27.18N 79.15W). The extrapolated minimum surface pressure was 983 mb. The aircraft flew outward to 27.74N 80.06W (along a radial with Melbourne radar), which was as long as time al
lowed, thus ending the pattern at 0204 UTC. Landing occurred at 0255 UTC at the Naval Air Station at Boca Chica.
Mission Evaluation and Problems
The mission was judged to be an overall success; however, it did point out the difficulties in timing an alert for the landfalling mission. The desired timing is such that during the mission the storm was less than 100 nm from the NEXRAD radar site. Thu
s, the time of landfall must be guessed accurately to make the most out of the flights along the radial between the radar site and the storm center. The optimum conditions were essentially met right at the end of the mission pattern of 950801I1.
The crews and the airborne radars performed well during the mission.
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