TROPICAL CYCLONE FORMATION: T.S. FIONA / MONITORING EATL
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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!
Conditions improved overnight for INVEST 98L and after becoming TD SIX briefly, and having run into a very breif period of slight dry air intrusion, the depression recovered nicely with cooling cloud tops again, and improved structure. Given this improvement, the NHC is now issuing advisories on newly formed Tropical Storm Fiona. This is the SIXTH Tropical Storm of the year. As of the 5:00 p.m. advisory from the NHC, the following was available on Fiona
5:00 PM AST Wed Aug 17
Location: 15.1°N 37.8°W
Moving: NW at 16 mph
Min pressure: 1006 mb / 29.71 in
Max sustained: 40 mph
Analysis of the CIMSS wind shear product from 18Z indicates FIONA has had the upper level anticyclone become more of an open, diffluent flow at the moment. The upper level wind product shows an outflow channel only from the eastern periphery, clockwise to the western semi-circle. This would explain the “tail” on the southern portion, extending westward. Current satellite loop imagery may indicate that upper level outflow is trying to improve, with the fanning out of the northern semi-circle. I believe this “hiccup” may have been temporary due to some slight intrusion of drier air. Current TPW however, indicates plenty of precipitable water within the system, and I believe FIONA may be able to mix out any small amount of drier air given this, and the extremely tight, small core. As just mentioned, satellite imagery indicates the structure to be slowly improving, and convection beginning to build once again, with a possible CDO feature trying to take shape.
The NHC mentions that upper level winds (wind shear) will increase from 72 hours, and beyond. The 12Z GFS NOAA RUC HFIP product does indicate this, however the updated 12Z wind shear forecast map indicates the upper level anticyclone becomes re-established, and upper level winds may remain conducive up to around 96-120 hours. This seems to be a strange discrepancy. However, based on the performance of the NOAA RUC product on EARL, I have to concur at the moment with the NHC. I currently agree with their intensity forecast, which is inline with the 18Z Intensity Guidance forecast, unless the cyclone hits the mid level dry air which is forecast, a little later in the period. Then, I would not rule out a slightly stronger storm.
NHC FORECAST INTENSITY
INIT 17/2100Z 15.1N 37.8W 35 KT 40 MPH
12H 18/0600Z 16.0N 39.0W 40 KT 45 MPH
24H 18/1800Z 17.0N 40.6W 45 KT 50 MPH
36H 19/0600Z 17.8N 42.1W 50 KT 60 MPH
48H 19/1800Z 18.7N 43.8W 50 KT 60 MPH
72H 20/1800Z 20.3N 47.4W 45 KT 50 MPH
96H 21/1800Z 22.6N 51.3W 45 KT 50 MPH
120H 22/1800Z 24.6N 55.0W 45 KT 50 MPH
FIONA is currently moving to the NW. This is in response to the cyclone still being relatively weak, and slight change on orientation of the sub-tropical ridge. The depression is moving due to a combination of two items…the flow of the ridge itself is pretty much oriented east to west…and a weakness in the ridge to the north to slightly east of north in the sub-tropical ridge. Based on these two factors, the updated steering layers forecast maps, and satellite cloud motion, It would be possible for the FIONA to make more of a slight bend toward the west (still moving WNW however) during the next 18 hours, and continuing WNW during the next 4-5 days as it moves through a break in the ridge which is forecast to occur near 50-55W. However, instead of recurving right away, at around 96-120 hours in the period, a small, reinforcing ridge develops far north of the system near 40N, keeping the system moving WNW, which is pretty much reflected in the NHC forecast track. Analysis of the 18Z dynamic guidance indicates the majority of the consensus modeling continues to shift slightly west with each run from 06Z this morning. The 18Z guidance reflects this. Based on this analysis, I would not be surprised to see a shift in track, more toward the west, which is now reflected in the NHC track at 5 days. I will be looking at this over the next few days, however will not have another update until late Sunday afternoon.
Elsewhere, I am monitoring the eastern Atlantic, as an area of disturbed weather associated with a tropical wave has just moved off the African coast. It appears the larger of the two (the one that was over the extreme western continent earlier) may have absorbed the smaller feature over the Cape Verde islands. This feature is noted with that “tail” to the west, around the southern portion, indicating good outflow. I will be monitoring this feature for any signs of development over the next few days.
The NHC as of the 2:00 p.m. TWO update, has designated a 20% probability of cyclone formation, for a tropical wave that should move off the continent on Saturday. This may be the feature in the EUMETSAT image located near 0N Longitude. Global model GFS, and the NASA GEOS model do indict another system to develop at around day days 5-6 in the period, bringing it closer to the Lesser Antilles as the track is forecast to be further south than what FIONA has taken, while the ECMWF keeps an open wave further north.
I cannot rule out development at the moment, as the current NASA GEOS TPW forecast calls for more moisture surges to exit Africa within the 3, 7 and 10 day forecast period, and the GFS and ECMWF indicating falling 500 mb pressure height anomalies in the 7-10 day period, as compared to current.
T. F. “STORM” WALSH III
GMCS, USCG (ret)
METEOROLOGIST / HURRICANE SPECIALIST /SEVERE WEATHER SPECIALIST
MEMBER WEST CENTRAL FLORIDA AMS