Tuesday, July 5, 2005

Considerable changes in the meteorological situation occurred overnight. T.D. #3 was upgraded to Tropical Storm Cindy, and 42 proceeded with its SFMR/fix tasked mission, taking off at 1330 UTC and planning to land in Key West. The most significant change was with the strong wave in the eastern Caribbean. Contrary to climatology, the system was named a tropical depression at 11 AM EDT on July 4. The forecast track had T.D. #4 moving WNW into the central Caribbean, crossing western Cuba and into the eastern Gulf of Mexico by day 5. It was forecast to reach hurricane intensity within a couple of days. Because of this forecasted track, we anticipated that one or probably both P-3's would be tasked for SFMR missions as the storm threatened the U.S. The T.D. was within range of the P-3 and the ER-2, albeit with a 3.5-hr ferry for the P-3. The system looked impressive on satellite imagery, with widespread deep convection, clear rotation in the midlevels, and well-defined upper-level outflow. However, the system was moving fairly fast (about 15-20 kt), and there was no indication of a closed circulation from the QuikScat. For this reason, we speculated that perhaps the system is not as intense as Dvorak estimates (the basis for NHC calling this a T.D.) would indicate. In the E. Pac, there was no likely candidate for genesis. Dora looked sheared apart near the coast, and the strong (20-40 kt) northeasterly shear was persisting over the E. Pac centered at about 100 W. A tropical wave was located at 97 W, however it was forecast to enter the high-shear zone and any genesis appeared highly unlikely.

With no candidate targets in the E. Pac or western Caribbean, with 42 on a tasked mission, and with a questionable tropical storm Dennis (T.D. #4 upgraded to Dennis at the 11 AM EDT advisory), we decided to abort our planned test flight coordination with the ER-2 and target Dennis in the eastern Caribbean. The pattern would be a figure-4 pattern, coming in from the west, along to the east, then a downwind leg, and then a north-south oriented leg. Leg lengths would be 100 nm, with four drops released evenly- spaced and a drop released each time the center point was traversed. The projected center point for the system (interpolated for 21 UTC) was 13.5 N, 67 W. Four BT's would also be dropped, one at 200 nm west of the center, then a combo drop at the IP 100 nm west, a combo drop at the center, and a combo drop 100 nm north of the storm. The P-3 would be coordinated with the ER-2. For the radial legs, the ER-2 would be offset by 10 nm, and for the downwind leg, the ER-2 would be vertically stacked with the P-3. The P-3 TA radar would be run in F/AST mode for the radial legs, and in continuous mode for the downwind leg. Return to San Jose at the end of the mission.

The plan is to fly Dennis with N43RF today as a full-duration 9.5 hour mission. Then 43 would fly it again tomorrow, again coordinated with the ER-2. Takeoff times would be similar to today, but the duration may be shorter because the system is expected to be closer to San Jose. N42RF is expected to land in Key West at around 6 PM EDT. From there we are considering tasking 42 for a research mission into Dennis with a scheduled takeoff of around 5 PM EDT on Wednesday 7/6. N42RF would then return to San Jose, landing at about 2 AM EDT on Thursday 7/7. N42RF would have a hard down day either Friday 7/8 or Saturday 7/9. In all likelihood the down day would be on Friday, since it will likely be tasked if the storm is threatening the U.S. N43RF would have a down day on Thursday, ready to fly on Friday.

It is possible that this set of flights could constitute an excellent set of IFEX missions, covering nearly the entire lifecycle of Dennis from immediate post-genesis through intensification and mature storm. The flights in the early stage of the lifecycle would be research missions, while the flights during the mature stage would be tasked missions.

The previous day's flight sampled Dennis just after it had undergone genesis. Peak flight-level winds of 45 kt were measured at 12,000 ft on the east side of the system, where the convection was primarily located. Close to 20 dropsondes were released in all quadrants of the system, and peak low-level and surface winds were about 35 kt in the east side of the system. The center of the tropical storm was relatively easy to located on the LF radar on the first (west-east) pass, but it became much more clear once the second (north-south) pass was completed, and the system was better organized as the pattern was completed. The coordination with the ER-2 worked fairly well for most of the pattern. The ER-2 was flown with a 12-nm offset to the right of the P-3 on the west-east leg, and then it was aligned to be vertically-stacked with the P-3 during the downwind leg. The problem with that leg was that the ER-2 was a bit behind the P-3 at the beginning of the leg (where most of the convection was located). By the time the ER-2 caught up with the P-3 and was vertically stacked, there was no convection in the area. For the final, north- south pass, the ER-2 was again offset to the P-3, this time to the left of the track. The turn point and the track was set to the original location of the center; however, Dennis had moved probably 10-20 nm from the time that center point was set. We began the north-south leg based on the outdated center location, and had to adjust the flight track midway through the leg. The ER-2 followed the P-3 in this adjustment.

All in all it was a good mission. The coordination with the ER-2 was good, and the communication between the P-3 navigator and the ER-2 pilot was excellent. We were able to collect radar, dropsonde, SFMR, and flight-level measurements from the P-3 in an early-stage tropical cyclone. There was plenty of scatterers, especially on the east side, to provide Doppler-derived wind fields, and we should be able to compare vertical motion statistics on the downwind leg with statistics derived from the ER-2, even though they were not vertically-stacked for much of that leg. This marked a positive beginning for the sampling strategy for Dennis, one that will include coordinated P-3/ER-2 measurements in a tropical cyclone in the Caribbean at nearly 24-h intervals from the earliest stage of its lifecycle, through its organizational stage, and until it is a mature, possibly major hurricane.

Rob Rogers
HRD Field Program director