TROPICAL CYCLONE FORMATION: INVEST 98L (90%)
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(T. F. “Storm” Walsh III)
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CURRENT 2016 ATLANTIC TROPICAL CYCLONE TOTALS:
TOTAL STORMS: 5
INTENSE HURRICANES: 0
StormW’s Seasonal Hurricane Forecast:
TOTAL STORMS: 13-15
INTENSE HURRICANES: 3-4
Good day everyone!
UPDATE: As of 2:00 p.m. EDT, the NHC has increased the probability of cyclone formation to 90%
Looking at the NHC Tropical Weather Outlook this morning, the NHC has increased the probability of of cyclone development in association with disturbance INVEST 98L, to HIGH (90%) during the next 5 days.
Based on information contained in the ATCF BTK product as of 12Z, the following was available on INVEST 98L:
8:00 AM EDT Tue Aug 16
Location: 10.2°N 31.4°W
Moving: W at 25 mph
Min pressure: 1008 mb/29.77 in
Max sustained: 30 mph
The disturbance is currently moving toward the west, to just north of west, with a 12 hour average speed of 25 mph. INVEST 98L is currently being steered by the southern periphery of the sub-tropical ridge. Based on analysis of the current steering layer mean, and forecast steering layers maps (00Z run, valid for 12Z), I expect this motion to continue during the next 24-36 hours, while continuing a slight gain in latitude. I will clarify something here at this time. Based on what information I had available to analyze yesterday morning, the forecast steering maps did not indicate a weakness in the ridge, therefor, I had to disagree at that time with the model guidance indicating a sharp WNW to NW turn. I still am in disagreement with the dynamic guidance to some degree at the moment with being too quick and too sharp as far as a NW turn. I do believe a persistent, more gradual gain in latitude will occur during the next 24-36 hours, prior to picking up a more northerly component. Based on the early model runs yesterday of the global modeling, it was unclear as to what the guidance modeling was picking up on. Analysis this morning did somewhat reveal what the dynamic guidance may be seeing now.
Based on analysis of the 500 mb anomaly maps of both the GFS and ECMWF, there are 2 notable weaknesses in the subtropical ridge. One to the NNE of 98L, and another further west located north of the Puerto Rico / Hispaniola area. Current steering is just beginning to show this slight weakness in the ridge, by the upward kink in the flow north of Puerto Rico. Albeit not strong, 98L is beginning to possibly “sense” this weakness, thus the slight gain in latitude. I mention possibly, as analysis of visible satellite loop imagery does indicate another possible weakness being created well north of 98L near 40W. Based on analysis of forecast steering at the moment, and the current developing situation, the north of west motion may continue during the next 24 to possibly 36 hours. Shortly after, a strong break in the ridge is forecast to occur near 45-50W. This should allow 98L to slow its forward speed, and begin more of the NW track from around 48 hours, onward, from 12Z this morning. Based on this, and what the forecast steering layers maps are showing, 98L, possibly Fiona by then, could perform a re-curve. At the moment, this appears to be the plausible scenario, albeit steering beyond day 5 does not indicate whether or not the ridge rebuilds. Based on this, I have to somewhat agree with the ATCF 12Z Dynamic guidance, however my thought is a slower turn, with more westward progression over the next 24 hours.
Satellite loop imagery indicates 98L has lost a good deal of convection over the past few hours, and looked a little more organized earlier this morning. Satellite loop imagery indicates there may be some slight dry air intrusion, albeit this may be temporary as the last couple of frames in the loop imagery seem to indicate 98L may be trying to become slowly better organized as higher cloud tops are being noted near the center in visible and RGB satellite loop imagery, and the system appears to starting to wrap up tighter.
Current wind shear analysis indicates a weak upper level anticyclone over 98L, with the shear forecast showing this feature to maintain itself for the next 4-5 days, before upper level conditions begin to become unfavorable. The NOAA RUC HFIP TC Diagnosis site indicates shear to remain below 15 kts as well, with an increase in wind shear at 120 hours.
Based on the probable track guidance, and forecast upper level pattern, I am calling for slow development of 98L, should dry air intrusion not affect the system. Based on current intensity guidance, guidance brings this to Tropical Storm strength in approximately 48 hours, and Hurricane strength in about 4 days. I cannot rule this out at the moment, however I feel intensification could be somewhat slower, given the current slight dry air issue, and lack of good organization at the moment.
Elsewhere, global models are in fairly good agreement at another area developing near the Cape Verde islands in around 4-6 days.
The wave train has become slightly more active, and I believe the area the models may be picking out is the large area behind the wave along the African coast at the moment, or the feature further over E. Africa. Development may be a good possibility, as the wind shear forecast indicates another upper level anticyclone to develop over the area in around the same time period. I will be monitoring this as well, should it come to fruition.
Analysis of the 500 mb anomaly maps of both the GFS and ECMWF lead me to believe we should see an increase in African waves by the last week of this month, as the forecast still calls for 500 mb pressures to fall over northern Africa, and 500 mb pressure anomalies becoming weaker (neutral heights) over the remainder of the continent, relative to higher pressure heights at this time.
The NASA GEOS dust and TPW forecast still indicates pretty much the same ratios over the next 3-10 days, with moisture surges still being indicated.
Elsewhere, Tropical Storm formation is not expected during the next 5-7 days
T. F. “STORM” WALSH III
GMCS, USCG (ret)
METEOROLOGIST / HURRICANE SPECIALIST /SEVERE WEATHER SPECIALIST
MEMBER WEST CENTRAL FLORIDA AMS