|Chief Scientist||Chris Landsea|
|Cloud Physics||Bob Black|
|Radar Scientist||Mike Black|
|Flight Director||Stan Czyzyk|
This document is divided into 3 sections (Each section is written by the Chief Scientist):
The goal of this mission was purely reconnaissance as Hurricane Lili was forecast to be within Cuban airspace, just south of the main island of Cuba and near the Isle of Youth. The Aircraft Operations Center (AOC) was tasked with providing 1800 UTC (October 17, 1996) and 0000 UTC (October 18, 1996) fixes of the storm. Because it was of hurricane strength, the reconnaissance flight was planned to be done at 5,000 ft making dropping sondes unnecessary. No special requests were made for sondes to be done. The planned flight path was the standard reconnaissance alpha pattern. As the mission briefing was completed right at 11am, I thought it would be helpful to obtain the National Hurricane Center (NHC) 1500 UTC forecast. Through Tom Strong's America On-line account, we were able to go to the NHC homepage and pull off the 1500 UTC Intergovernmental Discussion and Marine Advisory just a few minutes after 11am. This appears to be a reliable way to obtain the most recent NHC forecast guidance while over at AOC.
Hurricane Lili had winds of 65 kt at 1500 UTC with an estimated 989 mb central pressure. A moderate intensification of the storm was forecast before it made landfall on Cuba. Lili was moving to the north-northeast at 8 kt and was forecast to continue moving toward the north-northeast at about the same rate of speed for the next 12 hours. NHC (and the government of Cuba) had issued hurricane warnings for the Isle of Youth and the Western Cuba mainland provinces of Pinar Del Rio, Havana, Matanzas, Villa Clara and Cienfuegos. Additionally, a tropical storm warning was still in effect for the Cayman Islands, but no watches or warnings had been issued for the United States.
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We had anticipated a takeoff around 1600-1615 UTC to be able to provide the 1800 UTC center fix. However, a sheared starter caused the takeoff to be delayed until 1709 UTC. As we went up to 570 mb cruising altitude, we encountered what appeared to be the east side of a weak mid-tropospheric trough (see attached analysis). After flying over central Cuba, we descended to 5,000 ft and began the planned alpha pattern from the northeast side of the storm. Immediately we were encountering winds of at least 50 kt that gradually increased as we approached the storm. Accompanying these winds were widespread bands of stratiform rainfall with embedded lines of convective rainfall. However, hurricane force winds were confined to just within about 20 n.mi. of the center, within a convective band that was a partial eyewall. This partial eyewall only extended from the north-northeast side of the storm to the south-southeast side. Lowest extrapolated central pressure was 983 mb and highest winds were 71 kt on the northeast side at a radius (RMW) of 10 n.mi. (All five center fix data are presented below.) Unfortunately, the center fix was an hour late because of our delay in takeoff. With this position, it appeared that Lili was moving faster (~12-15 kt) and with a due north track between the 1500 UTC NHC position and our first fix at 1911 UTC. I was concerned that this continued motion to the north would force NHC to soon issue a hurricane watch for the Florida Keys, in the very least. On the southwest side of the storm, there was virtually no rain, stratiform or convective. 50 kt winds extended only about 20-30 n.mi. and gale force only about 50 n.mi. from the center. Overall, the reflectivities observed were generally 30-40 dBZ, with some cores up to 45 dBZ in the partial eyewall. Likewise, vertical velocities were moderate in this stage of Lili with infrequent peaks of 5-8 m/s.
The second center fix an hour and a half later (2045 UTC) showed that the intensity had not changed much, but that the northward motion continued though at a slightly slower pace (8-10 kt). Similarly to the northeast side, there was a large extent (at least 120 n.mi.) of 50 kt winds along the southeast side as well as a moderate coverage of stratiform and convective banding. Along the northwest side of the hurricane, no hurricane force winds were encountered, 50 kt winds were found only within about 20 n.mi. of the center and gale force out to about 50 n.mi. Overall, Lili presented a very asymmetric appearance both in the radar structure and in the wind fields - with the strongest precipitation and winds along the east side almost exclusively. We speculated that this structure was due to moderate westerly vertical shear.
During the remainder of the flight, the structure of the hurricane - in precipitation, winds and central pressure did not change substantially, with one exception. On the fourth penetration, however, the partial eyewall developed what looked like a mesoscale low along the northwestern portion of the eyewall (see notes for a drawing). Filaments of reflectivities around 30 dBZ were being wrapped around this mesolow on the north, then west, then south side until the mesolow was nearly completely defined by the reflectivity filaments on those three sides and the partial eyewall on the east side. The center fix for this penetration did find the lowest central pressure (and wind center) at the geometric center of this mesolow.
As far as the motion of Lili, by the third center fix the northward motion had virtually ceased and, subsequently, a slow eastward drift commenced. I was hoping that NHC was not forced by the first two fixes to initiate hurricane watches for the Florida Keys. As it turned out, NHC was able to not have to issue hurricane watches for the Keys or any other portion of the US (though they did issue tropical storm warnings as a sensible precaution for the storm). It was apparent though that with the extensive rainband on the eastern side of the storm that Cuba would experience - at the very least - problems caused by rainfall- induced flooding. At the worst, Cuba would have wind and surge damage, though we did not observed any significant change in the intensity of the hurricane during our flight.
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The mission was able to successfully provide center fix and flight level winds for Hurricane Lili just south of Cuba. The first fix, because of the delay in takeoff, was about an hour late. Two suggestions would be made for future reconnaissance flights: 1) utilize AOCs hookup to the World Wide Web to obtain the latest NHC advisories and the latest satellite pictures (good idea for any type of mission); and 2) consider rotating the alpha pattern after one complete run through to obtain legs along N, S, E, & W directions in addition to the NE, SE, NW & SW legs. Presumably, this would provide additional useful information for the NHC forecasters (as well as Mark Powell and Sam Houston's surface analysis). This suggestion was made in flight, but was not able to be implemented.
Take off delayed one hour due to sheared starter. Radar system "froze" up from 2116 to 2139 UTC.
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Return to mission page.
Return to Lili page.