Good evening everyone!
Tropical Storm Chantal continues to become slowly better organized, and most recently over the past 4 hours. As of the 8:00 p.m. EDT Intermediate Advisory from the NHC, the following was available on Chantal:
8:00 PM AST Mon Jul 8
Location: 11.8°N 55.0°W
Moving: WNW at 26 mph
Min pressure: 1010 mb / 29.83 in
Max sustained: 50 mph
CARIBBEAN SATELLITE LOOP
Chantal continues to move toward the WNW around the southern periphery of the sub tropical ridge. Based on satellite loop imagery, current steering, and forecast steering layers maps, I expect this motion to continue for the next 36 hours, before more of a bend just north of WNW occurs, in response to a weakness that begins to occur in the ridge near FL. and the SEUS. By days 4 and 5 (96-120 hours) as mentioned in the NHC forecast discussion, Chantal should slow and being a much slower motion toward the NNW, which is supported by the weakening steering flow in the steering layers forecast maps. Combined analysis of satellite loop imagery, forecast steering and model guidance, The GFS and CMC have two slightly different tracks. The GFS is more inline with the NHC track, and the CMC is further south, into south FL. by day 5. At the moment, I am discounting the CMC solution, as on the latest update of the forecast steering maps, the CMC has Chantal initialized a little too far south.
Based on these factors, I pretty much concur with the NHC forecast track up to day 5, however the track should begin to shift left, right thereafter as shown in the Dynamic Model Guidance for 00Z.
Chantal has become much better organized this evening. Analysis of the current and forecast wind shear maps indicates although shear maps and upper level winds maps have not really picked up on this, a careful reanalysis of satellite loop imagery indicates shear values to be relaxed enough that Chantal has become pretty much vertically stacked, and appears to be in the process of developing an upper level anticyclonic outflow aloft. This can be seen a little stronger now to the NE Quad of the storm, in the upper levels on satellite loop imagery.
The GFS Zonal Shear forecast indicates the Zero zonal shear value to remain over Chantal for the next 48 hours, until Chantal reaches Hispaniola. Based on this, I concur with the NHC intensity forecast. As she crosses the island, there should be disruption of the LLC. During days 4 and 5 in the NHC forecast, she becomes a depression. However, as she approaches the Bahamas, the current zonal shear forecast indicates wind shear values to drop expediently, with another small upper level anticyclone overhead until second landfall. Based on this, I will monitor that area closely for any regeneration of the system.
Elsewhere, it appears somebody doesn’t want me to take a break. The current run of the GFS model indicates another fairly strong development in the EATL in about 4 days. It appears this may stand a good chance at becoming Tropical Storm Dorian, and possibly our first Hurricane for the season. This feature can now be seen departing the African Coast.
I will have another update in the a.m.
T. F. “STORM” WALSH III
GMCS, USCG (ret)
METEOROLOGIST / HURRICANE SPECIALIST
MEMBER WEST CENTRAL FL AMS
CERTIFIED SKYWARN OFFICIAL STORM SPOTTER (advanced)