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Good evening everyone!
Tropical Storm Cristobal ids on the map. As of the 8:00 P.M. Intermediate advisory from the NHC, the following information was available on Cristobal:
Location: 24.6°N 73.1°W
Moving: N at 6 mph
Min pressure: 998 mb / 29.47 in
Max sustained: 45 mph
Cristobal in now moving very slowly to the north, and is following through a weakness in the subtropical ridge, and the eastern periphery of a ridge north of the New England area. The weakness is being induced by a deep layer trof digging southward, and is beginning to lift. This has caused the storm to slow it’s forward motion. In fact, Cristobal appears in the last few frames of satellite loop imagery to be almost stationary. Cloud tops had warmed earlier this evening, which is mentioned in the NHC Forecast Discussion (excellent discussion by the NHC BTW). However, it does appear cloud tops may be cooling in the last couple of frames in satellite loop imagery. It is not clear at the moment if this is just a pulse, or beginning of some slow strengthening trend. Imagery also indicates the COC may be getting much better defined with convection becoming more concentrated over or very near the center.
Based on my analysis of current and forecast steering layers maps, and water vapor satellite loop imagery, I concur with the NHC forecast track, and is inline with Dynamic Model Guidance which concurs with the continued, slow northward motion, and then a turn toward the NNE, then NE as an approaching trof from over near the Midwest U.S reinforces the weakness and takes the storm in that direction.
The current wind shear map indicates an upper level anticyclone is positioned to the west of Cristobal, which is allowing for only one outflow channel at the moment from the northern portion of Cristobal, in a semicircle to around the southern periphery of the storm. This should still allow for slow strengthening overnight, and during the next 48 hours. The zonal shear forecast indicates,as also mentioned in the NHC Discussion, for upper level winds to become more conducive thereafter, hence the NHC intensity forecast, to which I agree with.
From the NHC Advisory:
A TROPICAL STORM WARNING IS IN EFFECT FOR…
* CENTRAL BAHAMAS…INCLUDING CAT ISLAND…THE EXUMAS…
LONG ISLAND…RUM CAY…AND SAN SALVADOR
INTERESTS IN THE NORTHWESTERN BAHAMAS SHOULD MONITOR THE PROGRESS OF THIS SYSTEM.
I should have another update on Cristobal in the morning before I leave for work.
Elsewhere..ENTER Tropical Disturbance INVEST 97L.
INVEST 97L has been designated in the central Atlantic. As of the 18Z ATCF tracking information, the following was available:
Location: 11.0°N 33.15W
Moving: W at15 mph
Min pressure: 1010 mb / 29.83 in
Max sustained: 25 mph
The disturbance is moving toward the west at 15 mph. Based on analysis of forecast steering layers maps, I expect this motion to continue during the next 72 -80 hours. Thereafter, more of a WNW motion is indicated and agreed to in the steering layers forecast maps.
Based on analysis of current wind shear, upper level winds are not conducive at the moment. The current zonal wind shear forecast however, indicates in about 96 hours, upper level winds could become more conducive for slow development of this disturbance.
I will continue to monitor this system over the next 4 – 5 days as it moves in a general westward direction
I am out for the evening…Bedtime for Bonzo.
Have a blessed evening!
T. F. “STORM” WALSH III
GMCS, USCG (ret)
METEOROLOGIST / HURRICANE SPECIALIST / SEVERE WEATHER SPECIALIST
MEMBER WEST CENTRAL FLORIDA AMS
OFFICIAL SKYWARN SPOTTER (ADVANCED)