Discussion:
The large-scale environment remains dominated by a subtropical high in the eastern Atlantic and a stationary front in the western Atlantic and southeastern U.S. (Fig. 1). The NWS/TAFB analysis carries this front into Alabama, placing the remnants of TD#5 at the tip of the front. Several tropical waves are identified by TAFB, including some which have also been identified as pouches by PREDICT. These pouches are PGI29L, the remnants of TD#5 over southern Alabama; PGI27L, located at about 55W; PGI28L, northwest of the African coast at about 20N; and PGI30L, approaching the coast of Africa at about 13N and 8W. Of the two pouches where there is infrared satellite imagery available (Fig. 2), neither PGI29L nor PGI27L have significant deep convection associated with them, though PGI29L has deep convection to the south and west of the identified center.
A visible close-up of PGI29L (Fig. 3) shows indications of a circulation center in the scattered clouds near the border of Alabama, Georgia, and Florida. Almost all of the deep convection is confined to a region to the southwest of this circulation center, over the Gulf waters just offshore Mississippi and the Florida panhandle. A clear vorticity center is analyzed with this system (Fig. 4), and it remains located along the axis of a mid- to upper-level ridge oriented through Alabama and Georgia (Fig. 5). As a result of this positioning, the layer-mean flow is generally toward the south (Fig. 6), and all global models continue to bring this system over the Gulf of America in 1-2 days (Fig. 7), keeping it over water for 24-36 h. Both the ECMWF and GFS strengthen the system during this time (Figs. 8-9).
PGI27L is located near 15N 55W, and it is forecast to move toward the west into the Caribbean over the next several days (Fig. 10). The system is nearly devoid of any deep convection, and there is no indication of any vorticity associated with it based on the CIMSS analysis. Shear is low (Fig. 10), but dry air remains around the system and behind it (Fig. 11). Both the ECMWF and GFS keep the relative humidity low within the pouch and fail to develop it (Figs. 12-13). However, both models continue to maintain a trackable pouch out to 96+ h.
PGI28L has emerged off the coast of Africa and is currently located near 22 N 20W (Fig. 14). While the vorticity associated with this system was fairly well-defined yesterday, today the vorticity field consists of an elongated region of high vorticity extending far from the pouch center. All model guidance continue predict the system to move toward the northwest into very dry air (Fig. 15), where no development is predicted.
PGI30L is approaching the coast of Africa at 12N. It continues to be associated with some areas of deep convection (Fig. 16). Model guidance takes this system along a west-northwestward track for 2-3 days and then turns it more toward the west at 15-18 N (Fig. 17). The GFS predicts intensification of this system, with pouch-following diagnostics bringing the 700 hPa vorticity up to 10 x 10-6 s-1 and Okubo-Weiss exceeding 10 x 10-9 s-1 at 48-60 h (Fig. 18). Long-range GFS forecasts (Figs. 19-20) continue to indicate a well-defined tropical cyclone developing just off the African coast at about 15 N at 72h. This system is forecast to continue moving westward and intensifying somewhat out to 144h, or 6 days. The system being developed in the GFS may be PGI30L, or perhaps another, still unclassified system. Nevertheless, it bears watching for the 5-7 day time frame and beyond.
Mission synopsis:
No NOAA missions are planned in the next 24 h. We are focusing our attention on the remnants of TD#5, in the event that it re-emerges over the northern Gulf of America and develops into a tropical cyclone. A NOAA telecon may be scheduled for August 16 at 1430 UTC to discuss possible P-3 operations into this system beginning Tuesday at 20 UTC at the earliest.
A Global Hawk test flight is occurring Sunday morning and into the afternoon. After that, no flights are planned until at least the weekend as the dropsonde system is being integrated. The DC-8 has been placed on alert for a possible mission into the remnants of TD#5, should it emerge over water and develop into a tropical cyclone or at least provide a good target for instrument testing. Takeoff is currently scheduled for 15 UTC Aug. 17.
The G-V finished its shakedown mission into the southern tip of a front off the Florida coast at about 16 UTC Aug. 15. A possible follow-on flight is scheduled for tomorrow into PGI27L, with a scheduled takeoff time of 10 UTC. A final go/no-go decision is expected Aug. 15 at 20 UTC. A follow-on mission is currently planned the following take, same takeoff time.
Refer to http://grip.nsstc.nasa.gov/reporting/ for a spreadsheet showing these plans.
Robert Rogers
2010 IFEX Field Program Director
