Hurricane Iris
Vortex Motion and Evolution Experiment (VME)
(950829H Aircraft 42RF)

Scientific crew
Chief Scientist J. Gamache
Doppler Scientist M. Black
Dropwindsonde Scientist H. Willoughby
C-SCAT P. Black

This document is divided into 3 sections (Each section is written by the Chief Scientist):

Mission Briefing

See summary of 950829I for a general discussion of mission briefing. NOAA 42RF was to fly the inner flight pattern, staying within 45 nm of the storm center during the on-station portion of the flight. Take-off was to be timed to permit allow N42RF to be at the IP of 24.0N 64.87 W at 2245 UTC. N42RF would enter the storm from the west. This mission required coordination between Barbados, the location of N43RF, and St. Croix, the location of N42RF.

Mission Synopsis

N42RF took off from St. Croix at 212048 UTC. And proceeded toward the intended IP. As we approached the center it appeared that the storm center was nearly 1 degree farther to the south than expected, thus requiring some re-coordination of the aircraft . At 2250UTC, we headed into the center along a heading of 80 deg, from our new IP of 23.03N 65.05W, at a height of 7,000 ft to avoid the USAF aircraft at 5,000 ft. A fix had just been reported by the AF aircraft at 23.38N 62.12W, and our first fix was at time 2321 UTC, location 23.43N 62.15W, with an estimated minimum surface pressure of 972 mb. We found a maximum flight-level wind of 40 m/s on the W side of the storm. Our next pass was from N of the storm center to S of the storm center. A wind max imum of 48 m/s was found. At 2352 UTC, Parrish estimated storm center to be 4 minutes E of the closest point of approach (CPA), which was 23.48N 62.17W. A maximum wind speed of 40 m/s was found on the S side. The next pass was from SSE of the center t o NNW of the center. The center was found at 0017 UTC, location 23.47N 62.1W, with a extrapolated minimum surface pressure of 973 mb. Maximum wind speeds of 46 m/s and 41 m/s were seen of the SSE and NNW sides, respectively. The next radial flight leg was along a heading of 060 through storm center. The estimated center at 0053 UTC was 23.5N 62.1W, and the minimum SLP was estimated to be 975 mb. At 0057 UTC, the AF reported a fix of 23.52N 62.04W, with MSLP of 971 mb.

At 0119 UTC, N42RF began a circling pattern, waiting for the next coordination with N43RF. At 0127 UTC, N42RF began the second coordinated "4" pattern, heading 150 into the storm from 24.13N 62.42W. Our next center fix was 23.54N 62.05W at 0138 UTC. Ma ximum winds on the NNW side were 43 m/s. The next radial flight leg was on a 240 heading, the center being estimated at 23.58N 62.04W, time 0206 UTC. A radial leg on heading 030 began at 0219 UTC, and a maximum wind on the SSW side of the storm was 38 m/s. At 0230 UTC the center was fixed at 23.58N 62.02W. Next came a radial leg heading along heading 120. A center fix of 23.62 N 61.96W was made at 0302 UTC. Maximum winds were found to be 38 m/s.

At 0328 UTC N42RF began circling again to coordinate with N43RF as it returned from larger radii. The next radial leg began the final "4", starting from 24.18N 61.76W along a 210 heading. Maximum winds on the NNE side of the storm were 40 m/s, while the y were 36 m/s on the SSW side. The center was fixed at 0358 UTC, location 23.64N 62.00W. The final radial leg was coordinated with N43RF, and was along a 300 heading. The maximum winds on the ESE side of Hurricane Iris were 40 m/s and the storm positio n at 0433 UTC was 23.68N 61.54W. The pattern was complete at 0443 UTC, location 24.02N 62.65W, and N42RF landed back in St. Croix at 0609 UTC.

Mission Evaluation and Problems

This was a truly excellent mission from the point of view of execution. Coordination with N43RF went well, as did the listening to the ODW drops by N43RF with our 42's dropsonde receiving equipment. Finally, the radar system never went down, providing with excellent coverage of the evolution of the interior of Hurricane Iris, and data during all the coordinated radial penetrations with N43RF.

The intensity of Hurricane Iris during the mission was fairly steady state, although the structure evolved significantly during the 6 hours. What appeared to be the eyewall changed during the mission, and thus there where large apparent changes in eyewa ll diameter. Much further study will be needed to determine reasons for the very dynamic changes in radar presentation.