TROPICAL STORM FORMATION: TROPICAL DEPRESSION 9 / INVEST 95L / GOMEX DISTURBANCE
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*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: 8
INTENSE HURRICANES: 1
U.S. LANDFALLS: 2
StormW’s Seasonal Forecast:
TOTAL STORMS: 8
INTENSE HURRICANES: 1
Good evening everyone!
Tropical Depression NINE continues to be disorganized, and is moving slowly northward. Based on the NHC 5:00 p.m. AST advisory, the following was available on TD9:
5:00 PM AST Thu Sep 17
Location: 16.5°N 44.8°W
Moving: N at 7 mph
Min pressure: 1006 mb / 29.71 in
Max sustained: 30 mph
Satellite loop imagery shows that the LLC of the depression is exposed to the west of all the convection. The most recent wind shear product from CIMSS indicates the system is still under some 20-25 knots of westerly shear. Water vapor imagery indicates a good amount of dry air over or near the center.
Analysis of the wind shear forecast indicates shear will increase during the next 48 hours, with shear remaining constant in the forecast path. Based on current shear levels, the premise of shear increasing, and the presence of dry air, I agree with the NHC intensity forecast, however I feel that the depression may deteriorate a little quicker than forecast.
The depression is moving toward the north, slowly, and I expect this motion to continue for tonight, with a bend more toward the NNW tomorrow, followed by a WNW motion in about 3 days, as it heads into the weakness in the subtropical ridge. This is reflected in the dynamic model guidance, and the NHC forecast track. The forecast is for the remnant to be dissipated by that time.
ATCF TD9 AND INVEST 95L 18Z DYNAMIC GUIDANCE
Elsewhere, Tropical Disturbance INVEST 95L has changed little during the day. Satellite imagery indicates no further organization. Based on the recent ATCF FTP information, the following was available on INVEST 95L:
2:00 PM AST Thu Sep 17
Location: 12.5°N 33.7°W
Moving: WNW at 10-15 mph
Min pressure: 1010 mb / 29.83 in
Max sustained: 30 mph
Satellite loop imagery shows the system looking a little more ragged this evening. Water vapor loop imagery indicates the presence of some drier air, with a dry slot noted to the north, which seems to be wrapping in toward the center.
The current wind shear product from CIMSS indicates upper level winds are conducive for further slow development, and the current shear forecast indicates the 200 mb pattern to remain pretty much conducive during the next 96 hours. Thereafter, upper level winds are forecast to become a little less favorable, then marginal. It may be possible, once TD9 is out of the way, 95L may see some better conditions. Based on the current and forecast wind shear, we could see a Tropical Depression develop from this. However, this will be based on the premise of fighting off the drier air nearby. Based on the current intensity guidance, the 3 accurate models bring this to Tropical Storm status within the next 48 hours. This cannot be totally ruled out, however I am not totally in agreement at the moment, based on current structure and the presence of dry air.
18z INTENSITY FORECAST MODELS
INVEST 95L should continue moving toward the WNW during the next 72 hours, similar to TD9, before a more northward component takes place, as noted in the above dynamic guidance. Given the wild look of the forecast steering pattern however, I will be reanalyzing this to see if it holds.
Elsewhere, the area that global models have been hinting at off the SEUS coast in a few days, is sitting off the southern tip of FL. at the moment. This area is forecast to move NE across the Peninsula during the next couple of days. As it emerges along the SEUS coast, there could be a possibility of subtropical development. The NHC has designated a LOW (30%) probability of cyclone development during the next 5 days.
Given this feature is more baroclinic in nature, the forecast wind shear pattern is such that, (in which I concur with the NHC) upper level winds may become somewhat conducive for development of a subtropical cyclone. Albeit the forecast shows a lack of an upper level anticyclone, being the system is more baroclinic, the 200 mb streamline forecast indicates thee will be some divergence aloft. Secondly, the low is forecast to be located east of an upper level trof. Just as with an MLC (Mid Latitude Cyclone), the familiar low pressure systems you see on a weather map, low pressure forms to the east of an upper level trof. These types of systems are affected a little differently by wind shear, vice a purely tropical entity (barotropic low). I will be monitoring this area during the next 5-7 days for any changes in the pattern. Residents of Florida should be alert for flooding issued during the next 24-36 hours.
Have a blessed day!
T. F. “STORM” WALSH III
GMCS, USCG (ret)
METEOROLOGIST / HURRICANE SPECIALIST /SEVERE WEATHER SPECIALIST
MEMBER WEST CENTRAL FLORIDA AMS