Tropical storm Fiona

[Vorticity0123]

The 2016 Atlantic hurricane season has just given birth to a new system, being tropical depression Six. The tropical cyclone is a typical Cape Verde system, developing from a tropical wave that left the coast of Africa a few days ago. Satellite imagery shows TD Six has a well-organized satellite appearance, with a comma-like cloud pattern evident.

IR satellite image from TD Six taken around 06 UTC 17-08. Courtesy: Colostate University hurricane page

Such a cloud pattern is rather associated with a strengthening tropical storm than a tropical depression, so it would not be surprising if this system would be declared TS Fiona on the next advisory. In fact, CIMSS ADT satellite intensity estimates are suggesting Six already has 35 knot winds.

Another nice feature that can be seen on the image is a series of broken clouds to the northwest (upper right) of the depression. These clouds are stable stratocumulus clouds, which, as the name suggests, are indicative of dry, stable air associated with the Saharan Air Layer (SAL). Currently, the system is expected to move northwestward, or directly towards the stable and dry air. This will most likely prove to be quite a limiting factor on the future intensity of the depression. The NHC therefore only expects Six to intensify into a moderate tropical storm (with a maximum intensity of 50 knots).

NHC track forecast of TD Six as of 03:00 UTC.

Based on the forecast track, it appears that the only land area that is a potentially threatened by the depression is Bermuda. If it were to undergo extratropical transition, it might influence the weather in Western Europe in some fashion. However, this is all too far out to be concerned with at the moment.

 

Edited August 18, 2016 by Vorticity0123

[Nouska]

NHC now issuing advisories on tropical storm Fiona (can someone change title please).

TROPICAL CYCLONE GUIDANCE MESSAGE
NWS NATIONAL HURRICANE CENTER MIAMI FL
1846 UTC WED AUG 17 2016

DISCLAIMER...NUMERICAL MODELS ARE SUBJECT TO LARGE ERRORS.
PLEASE REFER TO NHC OFFICIAL FORECASTS FOR TROPICAL CYCLONE
AND SUBTROPICAL CYCLONE INFORMATION.
ATLANTIC OBJECTIVE AIDS FOR

TROPICAL CYCLONE FIONA (AL062016) 20160817 1800 UTC

Looking better this evening now that convection has fired again.

Still a bit further south than the models had initially suggested and there is still a bit of divergence between the GFS and ECM as a tweet from JB (Weatherbell) indicates.

 

[Vorticity0123]

10 hours ago, Nouska said:

Still a bit further south than the models had initially suggested and there is still a bit of divergence between the GFS and ECM as a tweet from JB (Weatherbell) indicates.

 

Much appears to be dependent on the intensity of Fiona, with a stronger system most likely ending up further north. With respect to intensity, it seems that Fiona will be having to go through a 'wall' of dry air on its west-northwestward track. As long as wind shear remains low, this air will penetrate the storm only occasionally. However, once wind shear kicks in (and according to the NHC that will happen in a couple of days) this dry air will be more easily entrained into the core of Fiona.

Saharan Air Layer analysis by CIMSS.

10 hours ago, Nouska said:

Looking better this evening now that convection has fired again.

Yes, it appears that the storm is able to sustain some convection over its center over the past few hours. It seems that dry air has not penetrated the system yet. There also appears to be a healthy amount of low level banding mainly to the north of te storm. So the circulation is reasonably well defined.

Finally, a CIMSS MIMIC (microwave imagery) loop of yesterday nicely showed the transition from a banding pattern (see first image of this post) to something looking like a partial eyewall on its eastern flank, and finally to a lack of any inner core features. As of now, it seems that some new inner core features have developed. This should become evident once new imagery comes in.

CIMSS MIMIC satellite loop of Fiona of 17-08