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  • Three research tasked (by HRD) NOAA P-3 missions were flown into Invest 96E in the East Pacific, in support of the Genesis Stage Experiment, part of the Hurricane Field Program - Intensity Forecast Experiment (IFEX). These missions were flown once daily out of Liberia, Costa Rica between 26 and 28 September, with takeoffs on the 26th. at 1600 UTC (10 AM local / 12 PM EDT), and at 1300 UTC (7 AM local / 9 AM EDT ) on the 27th and 28th. The P-3 ferried to Costa Rica on 25 September. While we were flying the first mission on 26 September, EP96 was only being given a "low" chance of formation in the NHC 2 and 5-day Tropical Weather Outlook (TWO). During the second mission, NHC increased the probability of genesis to "medium" and initialized the disturbance as "Invest" EP96. By the third mission, NHC increased the probability of formation to "high" as it was apparent that EP96 was likely to develop into a tropical cyclone within 48 hours. P-3 data contributed to NHC outlooks for EP96.

  • The sequence of flights will allow us to address Objectives #1 (Precipitation Mode) and #2 (Pouch) of the Genesis Stage Experiment. While the final mission on 29 September, which would have captured the structure of the developed storm (Tropical Storm Sergio), was cancelled due to a mechanical issue on the P-3, the previous three missions certainly captured EP96's structural evolution during its pre-genesis stage. Very few pre-genesis cases exist within the long history of the Hurricane Field Program, and the three missions flown could prove to be one of the best genesis datasets collected by the P-3. It's made even more unique by the fact that very little airborne data, in general, exists within East Pacific events.

  • Participating HRD P-3 Science Crew: Jon Zawislak (Lead Project Scientist, Radar Scientist, HFP Field Program Director), Rob Rogers (Lead Project Scientist, Radar Scientist), and Jun Zhang (Dropsonde Scientist) were on the P-3. Paul Reasor 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. NESDIS (IWRAP instrument) was represented by Paul Chang, Zorana Jelenak, and Joe Sapp.

  • A total of 52 dropwindsondes were launched over the three P-3 missions into EP96 (16 in 20180926H1, 18 in 20180927H1, 18 in 20180928H1). Sondes were released from an altitude of 14000 ft in 20180926H1, and at 12000 ft in 20180927H1 and 20180928H1. Altitudes were adjusted to accommodate data collection for the Imaging Wind and Rain Airborne Profiler (IWRAP) instrument. Some of the dropsondes released include IR sondes, which can also measure SST in clear conditions. 13 IR sondes were released of the 52 total during the missions (5 in 20180926H1, 4 in 20180927H1, 4 in 20180928H1).

  • A total of 7 Airborne EXpendable BathyThermograph (AXBTs) were launched from the P-3 into EP96 over the first 2 missions. The goal is to observe the surface fluxes, as well as validate satellite measurements of the SST. Unfortunately, the majority of these AXBTs did not report data. SST from the IR sondes could be used in place of these failed AXBT SST measurements.

  • The goal of the first mission, 20180926H1, was to survey the winds associated with the Papagayo Gap flow, as well as the disturbance to the west, with a box pattern. The Papagayo Gap flow is a region of enhanced lower tropospheric winds over the East Pacific (close to the coast) caused by funneling of flow through the Papagayo Gap of Nicaragua to the north of Costa Rica. They are thought to contribute to the spinup of a circulation. The westernmost northwest to southeast leg transected a surface trough associated with the developing disturbance.

  • The second (20180927H1) and third (20180928H1) missions were square-spiral patterns, which were planned to be centered on the apparent broad low-level circulation of the disturbance. The square-spiral design permits a gridded survey of dropsondes across the disturbance region, which will allow us to better identify the location of circulation centers up to flight level (12 kft). Wind and reflectivity analyses were also produced from the Tail Doppler Radar (TDR) (figures below), similar to what has been done for developed storms.

  • During both the second and third missions, we were able to identify a broad surface circulation within the grid from both dropsondes and the TDR analyses. In the third mission we were also able to identify a coherent mid-tropospheric mesoscale convective vortex (MCV), which is commonly found in the stratiform rain region of a mesoscale convective system (MCS). In this case, the MCS and associated MCV observed was on the eastern edge of the broad surface circulation, and very likely played a role in the eventual development of Sergio.

  • Although the P-3 missions were research tasked, TDR data was successfully transmitted to EMC for assimilation into HWRF for the 20180928H1 mission, when the Invest was already initiated (as well as the usual flight level and dropsonde observations) (no data was assimilated in previous missions as an Invest had not yet been initiated by NHC). TDR data from each flight was also provided for 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).

Sequence of P-3 TDR analyses showing composite reflectivity at 2 km for: 20180926H1, 20180927H1, and 20180928H1, from left to right

Sequence of P-3 TDR analyses showing wind speed at 0.5 km for: 20180926H1, 20180927H1, and 20180928H1, from left to right

Sequence of P-3 TDR analyses showing wind speed at 2 km (shading), as well as streamlines at 2.0 (black) and 5.0 km (grey) for: 20180926H1, 20180927H1, and 20180928H1, from left to right

Jon Zawislak
Field Program Director

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