2010 HFP IFEX forecast and mission planning discussion
July 6, 2010

The activity over the Atlantic basin is confined to a system in the NW Caribbean, AL96. This system consisted of a cluster of showers and thunderstorms with fairly cold cloud tops over the Yucatan channel near the peninsula (Fig. July6-1). These showers and thunderstorms have persisted for 24-36 h, and in fact looked even more impressive in terms of areal coverage and intensity the previous day. Looking back at ATCF fixes from the previous 2 days (Fig. July6-2), it is clear that the circulation center had been tracking generally west-northwestward and northwestward. This motion is generally consistent with the layer-averaged steering flow between 700 and 850 hPa (Fig. July6-3). The NOGAPS analysis of 850 hPa vorticity from the CIMSS web site (Fig. July6-4) showed a diffuse area of high vorticity that stretched from north of the Yucatan peninsula southward along the east coast of the Yucatan into Belize and Honduras. The upper-level winds showed a well-defined anticyclone over the Yucatan (Fig. July6-5), with low shear values in the middle of the anticyclone but higher shear values near 20 kt on the east side near the area of deepest convection (Fig. July6-6). The presence of the anticyclone aloft, the area of persistent, deep convection, albeit in a broad region, and the suggestion of cyclonic rotation in visible satellite animations all suggested that this was a system that had the potential to develop into a tropical depression. Numerical guidance also suggested, for some models at least, that development was possible. Both Decay-SHIPS and LGEM steadily intensified the system to strong tropical storm strength (Fig. July6-7). While both of these models already assume a tropical depression, which this system certainly was not at this time, the fact that they were developing it indicated that the system was in a favorable (or at least non-hostile) large-scale environment for development. It should be noted, however, that the dynamical models, including HWRF and GFDL, did not indicate development. Those models had been vacillating between no development and slow development to a tropical storm in several cycles leading up to 06 UTC July 6. Track guidance suggested a generally west-northwestward track, with the center being about 100 km offshore the Yucatan by 24 h after initial time at 06 UTC July 6 (Fig. July6-8).

Mission plan

For the reasons outlined above, it was decided to task the P-3 N42 for back-to-back missions, first takeoff at 20 UTC July 6 and subsequent takeoff for 08 UTC July 7, to conduct genesis missions into AL96. Also the G-IV was tasked for a research mission into the Gulf of Mexico and NW Caribbean to sample the large scale environment, with the goal of better specifying the large-scale shear environment and possibly sampling dry air that could impact the system. While the system was approaching land at the time the decision was made, it was felt that there was a reasonably-good chance that the circulation center would have emerged from the Yucatan by 00 UTC July 6, when the first P-3 mission would be arriving at the IP. The flight pattern would consist of a split lawnmower pattern, essentially traversing along the north and west coasts of the Yucatan and then down the east side of the peninsula. The follow-on P-3 mission would conduct a square-spiral mission over the system that was anticipated to have re-emerged off the north coast of the Yucatan into the southern Gulf of Mexico. Follow-on missions are planned, but they may be cancelled depending on the system structure to be decided at a conference call the following morning at 14 UTC July 7.

In addition to the meteorological and scientific reasons for tasking the P-3's mentioned above, it was felt that conducting these missions would be a good test of the system, as well as familiarizing the scientific crew with the aircraft, software, and personnel onboard the aircraft. This should help to streamline operations later in the season.

Rob Rogers
HFP Field Program Director 2010