Thursday, July 14, 2005

All three planes are available for flights starting today. Convection flared up over the target region during the overnight hours. Northeasterly shear is still evident over the region, preventing any development in the immediate future. The forecast situation shows that Emily has undergone a rapid intensification episode and is now a hurricane. It has entered the southeastern Caribbean sea, and the forecast has now shifted somewhat to the north, bringing the storm just south of Jamaica and predicting landfall further north along the Yucatan peninsula. The possibility of tasking for at least one of the P-3Õs is now higher, though it seems still unlikely that they will be tasked in the next several days.

In the East Pacific, the southwesterly flow persists, and QuikScat imagery suggests a cyclonic rotation south of the Gulf of Tuheanapec (see Fig. 1). Convection developed overnight in various regions; one associated with the suspected wave and other convection near the Gulf of Tuehanapec. Shear remains moderate over the region, but with the persistence of the southwesterly flow in the area, a cyclonic shear axis that arises as a result of flow, and the possible approach of another wave in the next 24 h, it still appears possible that genesis could occur after 2-3 days. The flight plan for N42RF calls for a survey pattern (see Fig. 2) where the plane will fly west along 10 N, from 89 to 97 W. Then it will turn NE to 12 N 93 W, then turn NW to 14 N 97 W. It will then turn east along 14 N to 92 W, then turn southeast to 12 N 90 W. Then S to 11 N 90 W, and finally east to 11 N 89 W. A total of 23 sondes are planned and 8 BTÕs. If there is any significant convective development along the way, the aircraft will deviate to map out the flow field associated with it, provided the deviation will not seriously alter the flow fields. The plane will fly at 14,000 ft. N43RF will fly a pattern that depends on what is found by N42RF. The takeoff for N43RF is scheduled for 05 UTC, and the ER-2 is scheduled to take off at 06 UTC for a coordinated mission with N43RF.

Along the flight of N42RF, there is not a clear sign of a shift in wind direction at flight level that may indicate a tropical wave at this altitude for the beginning of the flight (15,000 ft or 600 mb; see mission summary 050714H). Winds started out from 195 just offshore of Costa Rica, then switched to 225 about 200 nm offshore. Moving further west the flight-level winds turned to westerly, then generally stayed there for much of this part of the pattern. A visible satellite image (Fig. 3) shows generally isolated convection along the flight track, except for are an larger area of convection about 150- 200 nm south-southeast of the Gulf of Tuahenapec. N42RF may deviate from track somewhat to target this convection, if it remains and appears widespread by the time the aircraft reaches it. Upon passing 12 N, 93 W, there is a NW-SE oriented line of stratiform rain, with some convective elements embedded within it, about 10-20 nm to the southwest of the aircraft track. At 12.5 N 93.75 W, there was a pronounced wind shift from southwest to west-northwest at flight level. This may be indicative of the horizontal shear axis discussed previously, or it may be related to the rainfall seen off to the left of the aircraft. As flight has continued, it is evident that the flight-level wind field is rather chaotic along about 13-14 N. Multiple wind shifts have been detected, but in general there is northerly and northeasterly flow at flight-level west of 95 W and southwesterly flow east of there, especially closer to 90 W. A flare-up of moderate convective and stratiform rain did occur centered at 12 N 96 W while N42RF was in the pattern (Fig. 4). The aircraft flew within about 20 nm of the convection, so the tail radar should have sampled some of that. The vertical shear still appears to be moderate to somewhat high, so there are doubts as to whether this system will have a reasonable chance of developing. Future decisions on whether to deploy to Acapulco after tomorrowÕs flights will hinge on the likelihood of this developing. We may not want to go there if this is likely to just be a null case.

N43RF flew their mission with an 11 PM takeoff. They repeated the survey pattern flown by N42RF during the daytime mission.

Rob Rogers
HRD Field Program director