TROPICAL CYCLONE FORMATION: INVEST 99L (50%) / T.D. FIONA / 90L (100%)
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(T. F. “Storm” Walsh III)
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CURRENT 2016 ATLANTIC TROPICAL CYCLONE TOTALS:
TOTAL STORMS: 6
INTENSE HURRICANES: 0
StormW’s Seasonal Hurricane Forecast:
TOTAL STORMS: 13-15
INTENSE HURRICANES: 3-4
Good day everyone!
I wanted to touch briefly again on FIONA and INVEST 90L.
FIONA continues to have pulses of convection near her center, and is still barley at tropical depression status. Forecast conditions imply that shear may relax in a few days, and if she survives the dry air, could restrengthen slightly. However, given the amount of dry air, the NHC is maintain continuity (as there is disagreement in the models), and dissipates FIONA in 5 days. There is no change in track forecast thinking, as forecast steering still shows a break in the ridge, to which will steer FIONA more toward the north as indicated by NHC. Based on forecast steering however, after day 5, the possibility exists that what is left could stall briefly and meander in a weak steering regime.
INVEST 90L has been given a HIGH (100%) probability of becoming a depression soon.
Satellite loop imagery indicates 90L continues to become slowly better organized. As of the 12Z MTSCWA product, 90L was very close to closing off a LLC
The current wind shear product from CIMSS indicated a textbook upper level anticyclone over the system. Based on these factors, I believe the NHC may soon be issuing advisories on Tropical Depression SEVEN.
The current wind shear forecast indicates the upper level anticyclone will remain with 90L for the next 5-7 days, and current intensity guidance based on the majority of the models, brings 90L to hurricane status within 48 to 60 hours. Given the forecast parameters, I cannot rule this out, and concur with the forecast.
Forecast steering indicates a general west to WNW motion for the first 48-60 hours, with a turn to a more resembling NW by 72 hours and should maintain that motion through days 5-6 and possibly slowing as it feels the break in the subtropical ridge. This should eventually re-curve, and is reflected in the 12z dynamic model guidance.
What a difference about 12 hours makes. INVEST 99L has shown much improvement since yesterday. Satellite loop imagery indicates convection is now building close tot the center, and an increase in thunderstorm activity overall. INVEST 99L has gone from looking like a strewn out mess, to a more symmetric shape with an increase in clouds and moisture. RGB and visible satellite imagery did indicate a major increase in overshooting tops earlier, around the system.
Based on the 12Z ATCF BTK product, the following was available on 99L:
8:00 AM AST Mon Aug 22
Location: 15.4°N 48.9°W
Moving: WNW at 16mph
Min pressure: 1011 mb / 29.85 in
Max sustained: 30 mph
Analysis of the current shear product from CIMSS, indicates an upper level anticyclone centered just to the west of the system, and 99L SHOULD become positioned under this sometime today or tomorrow.
The improvement appears to be from what I mentioned in the second portion of my synopsis regarding 99L…The high amount of TPW, moving into the area of somewhat higher OHC, and improving shear conditions. Analysis of the forecast shear map from the GFS, and information from the NOAA RUC HFIP (Rapid Update Cycle…Hurricane Forecast Improvement Project) page, wind shear is forecast to remain 10 – 12 knots over 99L for the next 5 days, and then forecast to drop to 5 knots or less by day 6. The GFS forecast shear map indicates the upper level anticyclone to remain with 99L through the period. Should this come to fruition, 99L will be centered under the upper feature where zonal shear will be very close to zero.
However, FIONA is still close enough to cause some detrimental effect, in that some weak outflow boundary interaction may be occurring at the moment. However, based on visible and water vapor satellite loop imagery, this appears as if it may be decreasing. Current water vapor loop imagery shows 99L to be pushing the dry air west, in front of it. Given the amount of TPW, 99L may possible be able to over come the dry air. The current SAL image shows very minimal SAL near the system.
Based on these conditions and forecast conditions, and improved structure during the past 24 hours, I feel we may see some further, slow development regarding INVEST 99L, especially once far enough away from T.D FIONA. The 12Z intensity forecast models are still persistent in bringing 99L to hurricane or strong tropical storm status by day 5 in the forecast period. Should 99L continue to improve structurally, and begin to consolidate more, I cannot rule out the strengthening, albeit slow, as by day 5, guidance suggests 99L should be over the Bahamas, where Ocean Heat Content and SST’s are fairly high. Based on the 12Z MTSCWA product, 99L may be close to having a closed LLC.
Based on analysis of current and forecast steering layers maps, 99L continues to move in a generally west to slightly north of west direction. Based on forecast steering, I expect this motion to continue during the next 48 hours, with a more WNW track thereafter. By day 5 and 6, forecast steering indicates the system to be over the south to central Bahamas area, should the steering pattern maintain. From there, the guidance suggests the system could slow, and suggests that the western ridge is forecast to be over the eastern U.S., and begins to build over the system. Given that the scenario is 5-7 days out in time, forecast steering will have to be revisited very so often from now until then. However, this pattern would suggest a shift in guidance back to the left, or more toward the W – WNW, and is reflected in the 12Z dynamic guidance. Word of note, something amazing in the 12Z guidance…the Statistical modeling is pretty much in agreement with the Dynamic modeling.
Based on this recent change in the steering forecast, residents of the Bahamas and Florida Peninsula should monitor the progress of 99L, should it in fact become better organized and develop into a tropical cyclone over the next 5 days.
Based on analysis of the ECMWF TC Probability product, the model indicates another possible depression wanting to form off the African coast in days 8-10.
Based on today’s MJO and 200 mb Velocity Potential forecast, it still appears that we may have a very good increase in tropical activity during the next 5 – 10 days.
Have a blessed day!
T. F. “STORM” WALSH III
GMCS, USCG (ret)
METEOROLOGIST / HURRICANE SPECIALIST /SEVERE WEATHER SPECIALIST
MEMBER WEST CENTRAL FLORIDA AMS