Re: Tracking the Tropics: TS Gaston & INVEST 99L
Posted: Wed Aug 24, 2016 10:57 am
Morning briefing from Jeff (I've taken out non-99L references). No graphics (srainhoutx, if you want to post his discussion with graphics, please feel free to delete mine. I still haven't figured out how to resize down to post graphics):
99L:
Concern is growing that a tropical cyclone will move into the Gulf of Mexico late this weekend
99L this morning is over the northern Leeward Islands and while the system looks impressive on satellite images, surface observations show an ill defined surface low pressure system associated with the feature. The Barbados sounding yesterday evening showed two layers of dry air that are likely impacting the wave and helping to mitigate development in the near term. 99L is moving toward the WNW at 15-20mph and this motion is expected to continue bringing the wave across Puerto Rico Thursday and into the SE Bahamas Friday.
Track:
Much of the future track of this system will hinge on the large scale high pressure ridge over the SE US including how strong this feature is, how expansive, and where it is centered. Once in the south/central Bahamas, 99L will begin to feel the large scale high pressure centered near the Carolinas this weekend and will be forced to turn toward the west or even WSW approaching S FL or the keys. Effectively it appears that the door is closed on chances for the system to turn northward and recurve east of the US coast…this suggests a landfalling tropical system is increasingly likely on the US Gulf coast next week.
The next big question, once in the Gulf of Mexico which seems likely at this point, how far west does the system move before turning toward the NW and N and rounding the western edge of the Carolinas high pressure ridge. Global model ensemble support from the CMC, GFS, and ECMWF have all trended westward in the last 36 hours now showing a clustering well into the central Gulf of Mexico and potentially the central US Gulf coast. Operational model runs of these models have been all over the place with widely varied solutions of both track and intensity…but there is starting to be some growing consensus that the US Gulf coast is at threat.
The biggest aspect of the model guidance at this time is the westward trend and general overall placement and intensity of the large scale ridging over the SE US this weekend into early next week. One should not focus on the individual runs of each model, but their 500mb ridge pattern and their respective ensemble plots. Additionally models will continue to struggle until a define low level center develops and the development of this center could be many miles off of where current guidance is suggesting it will form due to the current poor organization of the wave.
Intensity:
Conditions will gradually become increasingly favorable for development as 99L moves toward the Bahamas this weekend. While there are a few factors in/near the Bahamas that could restrict development, the overall pattern appears favorable including generally light wind shear, high moisture levels within where the vortex should be located and very warm waters. This is where model support increases for development. As the system moves into the Gulf of Mexico conditions look ideal for development of a potentially significant tropical cyclone. An upper level 200mb high pressure cell (anti-cyclone) appears to encompass much of the central and eastern Gulf of Mexico with a westward moving upper level trough over MX/SW TX which could help with the upper level outflow and venting of a developing system. Sea surface temperatures are very warm…running in the mid 80’s and moisture looks plentiful. There appears to be little to stop intensification once in the Gulf of Mexico and the last 3 operational runs of the ECMWF have all shown significant growth over the Gulf.
Residents along the entire US Gulf coast and FL should closely monitor the progress of this system.
Review hurricane preparedness plans and be fully ready to enact these plans by late this weekend.
99L:
Concern is growing that a tropical cyclone will move into the Gulf of Mexico late this weekend
99L this morning is over the northern Leeward Islands and while the system looks impressive on satellite images, surface observations show an ill defined surface low pressure system associated with the feature. The Barbados sounding yesterday evening showed two layers of dry air that are likely impacting the wave and helping to mitigate development in the near term. 99L is moving toward the WNW at 15-20mph and this motion is expected to continue bringing the wave across Puerto Rico Thursday and into the SE Bahamas Friday.
Track:
Much of the future track of this system will hinge on the large scale high pressure ridge over the SE US including how strong this feature is, how expansive, and where it is centered. Once in the south/central Bahamas, 99L will begin to feel the large scale high pressure centered near the Carolinas this weekend and will be forced to turn toward the west or even WSW approaching S FL or the keys. Effectively it appears that the door is closed on chances for the system to turn northward and recurve east of the US coast…this suggests a landfalling tropical system is increasingly likely on the US Gulf coast next week.
The next big question, once in the Gulf of Mexico which seems likely at this point, how far west does the system move before turning toward the NW and N and rounding the western edge of the Carolinas high pressure ridge. Global model ensemble support from the CMC, GFS, and ECMWF have all trended westward in the last 36 hours now showing a clustering well into the central Gulf of Mexico and potentially the central US Gulf coast. Operational model runs of these models have been all over the place with widely varied solutions of both track and intensity…but there is starting to be some growing consensus that the US Gulf coast is at threat.
The biggest aspect of the model guidance at this time is the westward trend and general overall placement and intensity of the large scale ridging over the SE US this weekend into early next week. One should not focus on the individual runs of each model, but their 500mb ridge pattern and their respective ensemble plots. Additionally models will continue to struggle until a define low level center develops and the development of this center could be many miles off of where current guidance is suggesting it will form due to the current poor organization of the wave.
Intensity:
Conditions will gradually become increasingly favorable for development as 99L moves toward the Bahamas this weekend. While there are a few factors in/near the Bahamas that could restrict development, the overall pattern appears favorable including generally light wind shear, high moisture levels within where the vortex should be located and very warm waters. This is where model support increases for development. As the system moves into the Gulf of Mexico conditions look ideal for development of a potentially significant tropical cyclone. An upper level 200mb high pressure cell (anti-cyclone) appears to encompass much of the central and eastern Gulf of Mexico with a westward moving upper level trough over MX/SW TX which could help with the upper level outflow and venting of a developing system. Sea surface temperatures are very warm…running in the mid 80’s and moisture looks plentiful. There appears to be little to stop intensification once in the Gulf of Mexico and the last 3 operational runs of the ECMWF have all shown significant growth over the Gulf.
Residents along the entire US Gulf coast and FL should closely monitor the progress of this system.
Review hurricane preparedness plans and be fully ready to enact these plans by late this weekend.
