Mission Plan :

Fly TDR mission into Hurricane Leslie. Pattern will consist of a single Figure-4, with an IP on the NW side (Fig. 1). Two passes through the center will be executed, though there may be additional penetrations for IWRAP sampling if there is time. Drop combination sondes/AXBT at all turn and midpoints, plus the second center pass. Combo drop will also occur at the midpoint of the downwind leg, and on the NW and SE RMW drops. Sondes only will be dropped at NW and SW RMW drop locations. Fly at 10,000 ft radar altitude to start, then consider dropping to 7000 ft for IWRAP. The plan calls for 105 nm legs, but legs may be shortened on the east side to allow multiple passes for the IWRAP.

The storm is a minimal hurricane at time of planned takeoff. It is essentially stationary, with southwesterly shear as an upper-level anticyclone is displaced to the southwest of the storm and dry air likely impacting the system on the west side (Fig. 2). The precipitation is asymmetrically-distributed on the east/northeast side (Fig. 3,4). The Global Hawk was flying an outflow mission around the SE periphery of the storm (Fig. 5). This P-3 flight will provide inner-core measurements to complement the environmental measurements from the Global Hawk, even though the GH mission will be basically ending once we reach the IP.

Mission Summary :

The pattern was flown as planned. Takeoff was at 0812 UTC from Ft. Lauderdale. On the second inbound leg we reversed track for a second pass for more samples for the IWRAP (Fig. 6). Twelve sondes were dropped, but we did not drop RMW sondes because the RMW was thought to be at the end point. We also dropped 12 AXBT's. We descended to 8000 ft altitude after the first pass for better IWRAP measurements.

The mission did accomplish the objectives. The storm is weaker than thought. Precipitation was limited to the NE side, in a band of moderate precipitation about 75 nm from the center. The storm is basically stationary. AXBT's showed the lowest SST of 24.5 deg C near the center, plus a potentially isothermal layer of 24 deg C on the SW side of the storm that is at least 100 m deep. The peak SFMR winds were 54 kt, though there were winds of 83 kt at 935 hPa at the initial point measured from a dropsonde, indicating a sharp dropoff in the winds. This could result from a stable boundary layer in the presence of strong upwelling and ocean cooling. A composite of the two radar passes (Fig. 7) showed a broad circulation with peak winds on the NE and NW sides (Fig. 7). There is some indication of a possible outer wind maximum on the east side at 1 and 3 km altitude.

The aircraft completed its mission and landed at Ft. Lauderdale at 1714 UTC.

Mission Evaluation:

The mission did meet its objectives. This was the first mission into Leslie, and it showed a broad circulation with a significant decrease of wind speeds with height within the boundary layer. This drop-off may have been the result of a stable boundary layer in the presence of low SST's.

Problems :

There were no major problems. The sondes worked mostly fine, though is some cases the parachutes took some time to fully open. Doppler analyses were challenging with limited scatterers and potential quality control issues. A total of 12 GPS sondes were transmitted and 12 AXBT's were dropped.

Rob Rogers
Sept. 11, 2012