AL06 / FLORENCE MISSION HIGHLIGHTS

• Three research tasked (by HRD) NOAA P-3 missions were flown into Hurricane Florence, in support of the Early and Mature Storm Stage Experiments, part of the Hurricane Field Program - Intensity Forecast Experiment (IFEX). These missions were flown once daily out of Bermuda (last mission recovered in St. Croix) between 8 and 10 September, with takeoffs each day around 1200 UTC (20180908H1, 20180909H1, 20180910H1). While we were flying, Florence intensified from a 55 kt tropical storm to a 120 kt, Category 4 hurricane. Following these three missions, the P-3 was tasked by NHC to fly Tropical Storm Isaac for reconnaissance out of St. Croix, US Virgin Islands, and thus the P-3 did not fly additional missions into Florence.

• Participating HRD P-3 Science Crew: Jon Zawislak (Lead Project Scientist, HFP Field Program Director), Paul Reasor (Radar Scientist), and Heather Holbach (Dropsonde Scientist) were on the P-3. Nancy Griffin, Joe Griffin, and John Gamache provided ground radar science support for the P-3 missions. The ground support assist in the transmission of the Tail Doppler Radar analyses from the aircraft to EMC and NHC.

• In addition, 9 NHC-tasked G-IV synoptic surveillance flights sampled the environment surrounding Hurricane Florence (20180908N1, 20180909N1, 20180910N1, 20180910N2, 20180911N1, 20180911N2, 20180912N1, 20180912N2, 20180913N1).John Gamache and Paul Reasor provided ground radar support to process and transmit G-IV Tail Doppler radar data to EMC.

• HRD has been contributing towards modifications of the G-IV synoptic surveillance pattern to include an "inner" 90 nmi circumnavigation and Florence is the first storm in which this modification was adopted. Therefore for some of the missions in which this was flown, the G-IV TDR was able to detect more precipitation than usual, and thus useful wind measurements were sent to operations (NHC and AWIPS-II, as well as EMC for assimilation into HWRF).

• For three of the G-IV missions, Brittany Dahl, a UM/CIMAS/HRD scientist, provided on aircraft dropsonde processing support. AOC currently has a shortage of Flight Directors, and at the beginning of the season requested the help, as needed, for dropsonde processing on operational missions. This is the first time this support was requested and HRD was able to respond to this request.

• A total of 86 dropwindsondes were launched over the three P-3 missions into Florence (19 in 20180908H1, 24 in 20180909H1, 43 in 20180910H1). Most of the sondes were released from an altitude of 8000 ft. 4 sondes were released from 20 kft during a partial circumnavigation at about 90 nmi to the west of the center during the 20180908H1 mission, while the storm was an asymmetric tropical storm. Six sondes during 20180909H1 and 24 sondes during 20180910H1 were released near the radius of maximum wind in the eyewall, in support of the NESDIS Ocean Winds Experiment.

• A total of 20 Airborne EXpendable BathyThermograph (AXBTs) were launched from the P-3 into Florence over the 3 missions. The goal is to observe the surface fluxes within the inner core, and particularly within the maximum wind regions of the storm.

• A total of 281 dropwindsondes were launched over the nine G-IV missions into Florence.

• Although the P-3 missions were research tasked, all Tail Doppler radar data was successfully transmitted to EMC for assimilation into HWRF (as well as the usual flight level and dropsonde observations), as well as into AWIPS-II, where the NHC Hurricane Specialists were able to view the data in near real time (within about 1.5 hr after data collection).

• Missions fortuitously coincided with the initial intensification, and onset of rapid intensification of Florence. Florence had previously been a Category 4, but weakened in the days previous to the flights due to high vertical wind shear. During the first mission (20180908H1) Florence was a tropical storm, with initially the surface center exposed, but during the mission showed signs of increased organization through an improvement in the precipitation symmetry within the inner core. It intensified from 55 to 60 kt. During the second mission (20180909H1), Florence was a minimal hurricane, 65-70 kt, throughout the mission, but it was apparent through additional increases in organization that the storm (given the also favorable environmental conditions), was likely to soon experience rapid intensification. The mission on 9 September did, in fact, uniquely provide critical measurements right at the onset of a subsequent RI event. By the third mission (20180910H1), Florence had intensified rapidly to a 120 kt hurricane.

• The partial circumnavigation to the west of the storm during 20180908H1 was to sample the asymmetry in the precipitation, however that asymmetry, by the time of the mission, was primarily to the south. Regardless, we were able to exercise flight at 20 kft in the storm environment, predominantly, though, staying in a region in which we were able to maintain visual meteorological conditions (VMC). This module was part of the Early Stage Experiment, Science Objective #1 (AIPEX), as well as to provide some continuity with the following G-IV missions, which were designed to fly (for the first time) the inner 90 nmi circumnavigation.

• The NESDIS Ocean Winds team (for their IWRAP instrument) were able to achieve 2 additional penetrations on 20180909H1 and 6 additional penetrations on 20180910H1 in the high wind regions of the storm. They dropped radius of maximum wind sondes.

• The initial SW to NE passes in the butterfly were designed to parallel CYGNSS tracks anticipated to go through those regions around the time of our arrival to the storm (~1400-1430 UTC each day). We were a bit late on 20180908H1 (~30 min), hit the target time on 20180909H1, and missed by a considerable time (> 1 hr) on 20180910H1. The hope of the NESDIS Ocean Winds team was that these CYGNSS tracks would pass through the high wind region of the storm, and that our pass would align in both space and time for validation purposes.

Sequence of P-3 TDR analyses showing composite reflectivity at 2 km (top row) and wind speed at 0.5 km (bottom row), for: 20180908H1/2, 20180909H1, 20180910H1, from left to right

Sequence of G-IV TDR analyses showing composite reflectivity (top two rows) and wind speed at 0.5 km (bottom two rows), for: 20180909N1, 20180911N2, 20180912N1, 20180912N2, 20180913N1, from left to right

Jon Zawislak
Field Program Director

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