Forecast scenario
The target for today remains AL96, which has moved off the northwest section of the Yucatan peninsula. Infrared imagery at 1215 UTC (Fig. July7-1) shows that the circulation that had been sampled during the previous two missions has limited precipitation associated with it. Some cloud tops as cold as -60 C are located along the western periphery of the circulation, estimated to be at about 21 N 91 W at this time. But in general widespread deep convection has not been associated with the system for several hours.
The previous two flights had documented a fairly broad circulation between about 1.5 km and 2.5 km altitude. Figure July7-2 shows a composite of dropsondes and radar analyses for the first two P-3 flights at 0.5 to 2.5 km altitude, with an interval of 0.5 km. From these plots it is clear that a circulation is most evident at 2 and 2.5 km altitude, though by the time of the second flight there is some indication of a circulation at 1.5 km altitude as well. It appears that the circulation may have been tilted toward the southeast with increasing altitude. Interestingly, two drops on the extreme northwest portion of the pattern during the second flight suggested a small circulation at 0.5 km altitude. The location of this circulation is roughly consistent with where NHC was placing the center of the system based on satellite examination of low-level cloud motions.
Large-scale analyses of vorticity, based on the NOGAPS model and satellite-derived winds, do not capture these details, but rather depict an elongated vorticity maximum oriented NNW-SSE from the northwestern Gulf of America to the Yucatan peninsula (Fig. July7-3). Upper-level winds generally show weak flow over the system (Fig. July7-4), though the clear anticyclone seen in the previous day is not evident today. The 850-200 hPa shear (Fig. July7-5) shows a sharp shear gradient to the east of the system, but generally weak shear 10 kt over the system itself. One possible explanation for the lack of deep convection associated with the system is the presence of relatively cool waters off the northern tip of the Yucatan (Fig. July7-6). Further north and west, however, the sea surface temperatures warm up to near 28 C, suggesting that as the circulation continues to move to the northwest convection may flare up again. This is infact the case, as visible and infrared satellite imagery shows that convection started to redevelop within and near the midlevel circulation center by 2045 UTC (Figs. July7-7 and July7-8). Model guidance at 12 UTC was generally consistent in predicting a west-northwest track of the system, bringing it within about 100 km of the coast by 24 h (Fig. July7-9). Intensity guidance continued to predict slow strengthening, but any significant intensification is not likely due to the proximity to land (Fig. July7-10). Mission plan
With the system in a lower-shear environment and likely to encounter warmer sea-surface temperatures, N42 was tasked for a follow-on IFEX genesis experiment, with a take-off at 20 UTC July 7 and a follow-on for 08 UTC July 8. The G-IV was also tasked for a follow-on mission, take-off at 1730 UTC July 7. The flight patterns for the P-3’s would consist of square-spiral patterns (see 2010 HFP plan) centered on the location of the low-level center. If there is a clear area of vigorous, deep convection located generally within the circulation, a convective burst module would be attempted. The G-IV pattern would sample the upper-level cyclonic circulation in the western Gulf of America and the upper-level flow on the north side of the system.
Rob Rogers
HFP Field Program Director 2010
DISCLAIMER: The above discussion is intended to provide a brief summary of recent and future HRD Hurricane Field Program Operations. Any use of this material beyond its original intent is prohibited without permission of the HRD director. Media inquiries should be directed to Erica Rule (305-361-4541 or Erica.Rule@noaa.gov, Evan Forde (305-361-4327 or Evan.Forde@noaa.gov), or Jana Goldman (301-713-2483 or Jana.Goldman@noaa.gov).
