Tropical Storm Fiona projected to pass North



Last Updated: 8/17/2016, 5:00:00 PM (Eastern Daylight Time)

  • Location: 15.1N 37.8W
  • Movement: NW at 16 mph
  • Wind: 65KPH
  • Pressure: 1006 MB
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

Source: Weather Underground