Hurricane Hortense

Hurricane Hortense Reconnaissance
(960911I1 Aircraft 43RF -- single aircraft)

Scientific Crew

Chief Scientist -- Michael Black

Radar/Doppler Scientist -- Steve Feuer/Michael Black

Cloud Physics -- Steve Feuer

Workstation -- Paul Leighton

Air Chemistry -- Stan Gedzelman (CCNY)

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

Mission Briefing

This was a NHC/TPC-funded reconnaissance mission with HRD personnel along for the ride. In addition to the collection of flight-level, radar, Doppler, and Cloud physics data, the flight provided an opportunity for training and for collection of rain/water vapor samples for an ongoing air-chemistry project that HRD supports. The project is headed by Jim Lawrence of the University of Houston and Stan Gedzelman from the City College of New York. HRD crew members and Stan flew to Tampa, Florida in the evening of 10 September for a flight from MacDill AFB into Hortense on the 11th. Takeoff was scheduled for 1500 UTC with a standard "alpha" pattern to be flown at 5,000 ft. No ODW's were available to use on the flight and NOAA42 was scheduled for similar mission later that evening.

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Mission Synopsis

Takeoff was at 1454 UTC when NOAA43 turned to the southeast to penetrate Hortense's eye near the Turk and Caicos islands of the Bahamas chain. At 1712 UTC we were at our initial point for the pattern, 150 nmi NW of the eye. The northern portion of the eyewall was visible on the LF radar. Upon nearing the storm center, the radar images showed that Hortense had a hub cloud in the northern semicircle of the eye that was probably the remains of an inner eyewall. The hub cloud was surrounded by an outer eyewall that was ~40 nmi in diameter and which was open on the south side. After passing though the outer (main) eyewall that contained >40 dBZ reflectivities, moderate vertical motions and 95 knots at flight level (5,000 ft), we found the 970 mb center at 1753 UTC near Grand Turk Island at 21° 36' N, 70° 44' W. After passing through weak and shallow convection on the SE side, NOAA43 turned north for a downwind leg about 150 nmi from the center. Our next inbound leg, from the NE to SW found a series of stratiform rainbands in the NE quadrant and the eyewall was observed to have 105 knots of wind. The central pressure at 1920 was down slightly at 969 mb and Hortense had moved to the NW to 21° 47' N, 70° 48' W. The hub cloud had all but disappeared and the main eyewall had constricted to 35 nmi diameter, but was open along the south and southwest sides. The wind maximum on the SW side was about 75 knots in clear air. The sea-state was clearly visible and was spectacular with surface winds blowing at an estimated 65 knots. Our next to the last pass into Hortense was from the southeast where again the eyewall was open and winds of 100 knots were observed in the clear air. Hortense was deepening, with the central pressure falling to 967 mb at 2037 UTC. After a downwind leg 150 miles on the west side of the center, we headed for the eye from the SW quadrant. The sea-state was impressive again in the partially-open SW eyewall. Hortense continued to deepen and move to the NW as our last center fix found 965 mb at 2203 UTC at a location of 22° 9' N, 71° 3' W. The eye had contracted further having a diameter of ~20 nmi. Our exit through the NW eyewall provided the most excitement, with strong vertical motions and flight-level winds of 115 kts. Our ferry back to MacDill was uneventful and we landed at 0044 UTC.

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Mission Evaluation and Problems

This reconnaissance mission provided a good opportunity to collect valuable data at a minimum cost to HRD and to provide training and data collection for an HRD-supported air chemistry project. Steve Feuer was given additional training on the operation of the cloud physics and radar stations. Paul Leighton used the HRD-developed workstation to provide radar images, in real-time, to forecasters at NHC/TPC. Sam Houston and Mark Powell of HRD used the flight-level data with their analyses software to overlay surface-wind field plots on the radar images and provided them to the forecasters. The data collected will be useful in HRD's ongoing mesoscale and convective-scale research projects.

The radar system was down occasionally for brief periods near the beginning of the flight, but never during important data collection times. Otherwise, the equipment and AOC crew performed admirably.

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