BULLETIN
TROPICAL STORM FIONA ADVISORY NUMBER 4
NWS NATIONAL HURRICANE CENTER MIAMI FL AL062016
500 PM AST WED AUG 17 2016
...DEPRESSION STRENGTHENS INTO SIXTH NAMED STORM OF THE SEASON OVER
THE CENTRAL TROPICAL ATLANTIC......
SUMMARY OF 500 PM AST...2100 UTC...INFORMATION
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LOCATION...15.1N 37.8W
ABOUT 920 MI...1480 KM W OF THE CABO VERDE ISLANDS
MAXIMUM SUSTAINED WINDS...40 MPH...65 KM/H
PRESENT MOVEMENT...NW OR 305 DEGREES AT 16 MPH...26 KM/H
MINIMUM CENTRAL PRESSURE...1006 MB...29.71 INCHES
TROPICAL STORM FIONA DISCUSSION NUMBER 4
NWS NATIONAL HURRICANE CENTER MIAMI FL AL062016
500 PM AST WED AUG 17 2016
During the past 6 hours, the tropical cyclone has made a transition
from a large outer banding pattern to more of a CDO-type feature.
Also, a 1635Z SSMI overpass confirmed the tight inner-core structure
noted in the two earlier ASCAT passes. Dvorak satellite intensity
estimates are T2.5/35 kt from TAFB and SAB, and a 1225Z ASCAT-A
overpass indicated winds of near 35 kt at that time. Based on these
data, the initial intensity is increased to 35 kt and the cyclone is
upgraded to Tropical Storm Fiona.
The initial motion estimate is 305/14 kt. The latest model guidance
has come into much better agreement with the previous track
forecast, with the GFS model shifting a little farther south and the
ECMWF making a significant shift to the north due to that model not
weakening Fiona as much now as compared to previous forecast cycles.
These model changes have resulted in a northward shift in the
consensus models TVCN and GFEX. Given the much better agreement in
the NHC model guidance, the new track forecast was only shifted
slightly southward of the previous advisory track after 72 hours in
order to move closer to the consensus models.
There are no significant changes to the previous intensity forecast.
Fiona is a compact tropical cyclone with a radius of maximum winds
of 15 nmi or less, which makes the storm susceptible to sharp
fluctuations in intensity. The aforementioned SSMI satellite pass
also indicated that the small inner-core region of Fiona now appears
to be insulated from the very dry mid-level air that had earlier
eroded the cyclone's convection. That, along with low shear
conditions and marginal SSTs near 27C, should allow for some gradual
strengthening for the next 36-48 hours, assuming that the cyclone
can mix out any occasional intrusions of dry air. By 72 hours, the
vertical shear is forecast to increase to around 20 kt from the
southwest, which should act to arrest the intensification process
and perhaps even induce some slight weakening. However, by 96 hours
and beyond, the shear is forecast to steadily decrease when the
cyclone will be moving over SSTs greater than 28C. These conditions
could allow for the compact cyclone to maintain a steady intensity
despite being embedded in mid-level humidity values of near 50
percent. The official intensity forecast is similar to the previous
advisory and closely follows the intensity consensus model IVCN
through 48 hours, and then lies just below the Decay-SHIPS model at
72-120 hours.
FORECAST POSITIONS AND MAX WINDS
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
$$
Forecaster Stewart
NNNN
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. Now the question is, what will she do?
This sums it up in a nutshell. Dry air all around the cyclone and shear awaiting it as well. For me, does not look promising for Fiona at this time.
