SEVERE WEATHER THREAT: SLIGHT
TROPICAL STORM FORMATION: DANNY
ALL forecasts contained on this site, are based on my analysis and knowledge of various forecast tools, including information contained in NHC products, and are not copies from any other entity.
*NOTE: In the TROPICAL STORM FORMATION line above, probabilities are for during the next 5 day period. My personal probability will be listed as either NONE, MONITORING or PROBABLE. This does not necessarily mean something will develop, but that certain forecast conditions are likely to be present, favoring development. Once NHC products become available, then the appropriate probability and percentage will be used.
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Current Storm Total for 2015:
TOTAL STORMS: 4
INTENSE HURRICANES: 0
U.S. LANDFALLS: 2
StormW Seasonal Forecast:
TOTAL STORMS: 8
INTENSE HURRICANES: 1
Good evening everyone!
All I can say is WOW! What a difference 24 hours makes. Although I wasn’t too surprised as far as development, but am somewhat taken by how quick the ramp up was, given everything I had looked at in analysis last night. Enter into the MDR, Tropical Storm Danny! Being development as a depression occurred at 36.5W, I do not know if the NHC will designate this a Cape Verde system, as it may have just missed the criteria of being within 600 of the islands.
As of the 5;00 p.m. EDT advisory from the NHC, the following was available on Tropical Storm Danny:
Location: 10.9°N 37.5°W
Moving: W at 12 mph
Min pressure: 1008 mb/29.77 in
Max sustained: 40 mph
Danny looks rather impressive on satellite imagery this evening. Banding has become much more pronounced over the past few hours, and an established outflow is noted. I do believe I spoke of this yesterday evening, in that if last nights disturbance could continue with the trend, it could begin to establish an upper level anticyclone over itself. This is also mentioned in the NHC Forecast Discussion.
Danny is currently moving toward the west, or just north of west at 280 degrees according to the NHC. This motion is due to the steering flow just to the north of the storm, and a small weakness in the subtropical ridge. I have drawn a red circle in the satellite image where the weakness is noted, and is linked to the loop feature. Just click on the graphic, and you can get an idea of the steering flow.
Based on my analysis of the current and forecast steering layers, and combined with information contained in the NHC Forecast Discussion, I expect this general motion to continue for at least the next 72-96 hours. Thereafter, forecast track will depend on how strong Danny can become, and how quick the subtropical ridge may build back in north of the storm. Based on information in the NHC Forecast Discussion, the ridge may build back according to the ECMWF, which leads to the NHC forecast track solution. Given the fact the GFS did not initialize the system accurately today, this means the consensus models are off. Based on this, I concur with the NHC forecast track. This could change prior to the end of the forecast period, as the atmosphere is continually changing…but at this moment, the official track contained in the above tracking map looks good.
Again, Danny continues to become slowly better organized. In fact, recent loop imagery indicates what may be a CDO, and colder cloud tops that appear to be starting to coalesce around the center of circulation. NHC did indicate that microwave imagery indicated a well developed low and mid level structure.
The current wind shear map did indicate the upper level anticyclone feature over Danny, with very low shear values.
The latest wind shear forecast from the GFS, which has handled the shear forecast for Danny thus far, in an exemplary manner, indicates upper level winds should remain conducive for further slow development. The hindrance may still be some slight dry air intrusion. However, as I addressed last night, especially in some of the weather groups I am in, with noting the rapid expansion of the moisture field yesterday evening, given that Danny has a well developed structure and is fairly compact, slight dry air intrusion should be able to be mixed out. This would be the most likely reason for the slower development.
Based on the premise of only a slight hindrance of dry air, and improving structure in satellite loop imagery, I look for Danny to become a hurricane during the next 36-48 hours.
Based on these forecast parameters, I have to concur with the NHC Intensity Forecast for a Category 2 hurricane near the end of the forecast period. Looking into the shear forecast past that time becomes less accurate, however as Danny approaches the islands, the GFS is indicating around days 7 -8 that wind shear could relax to 10-15 knots in the eastern Caribbean, but with somewhat of a little less favorable outflow pattern. Let’s hope the pattern can weaken Danny by then, as there is some high heat content in the Caribbean.
All interests in the Windward and Leeward islands should closely monitor the progress of Danny during the next 5 days for any significant changes. I will continue to monitor Danny during the next 72-96 hours for any significant forecast changes to the steering pattern and upper level pattern. I will also be watching any subsequent tropical waves for signs of development, and an area near Bermuda, which has a slim chance at developing subtropical features.
Elsewhere, Tropical Storm formation is not expected during the next 7 days.
Have a blessed evening!
T. F. “STORM” WALSH III
GMCS, USCG (ret)
METEOROLOGIST / HURRICANE SPECIALIST / SEVERE WEATHER SPECIALIST MEMBER WEST CENTRAL FLORIDA AMS