FLHurricane.com: Subtropical Storm Sandwich Anyone

Most of the reliable global models continue to hint development of an or subtropical feature later next week either in the NW Caribbean, SW Atlantic or SE Gulf of Mexico. Currently there is a suspected surface trough south of Cuba (75W-80W) that continues to interact with cyclonic mid-upper level winds to produce moderate to strong showers and thunderstorms over the NW Caribbean, Cuba and Jamaica that has increase in organization and spatial extent. This trough is expected to track towards the northwest, roughly parallel to the coast of Cuba, becoming more amplified as a surface low builds towards the surface over the next several days. This trough/low is then expected to interact with an advancing surface cold front. As the frontal trough secludes, there becomes the possibility that a subtropical cyclone may form under a broad upper low. Currently, there are little signs of a surface low as of yet, with a 5-knot westerly wind reported at Kingston, Jamaica but nothing on a synoptic scale.

Most of the models do take this feature into a region that is marginally favorable for development with warm sea surface temperatures, modest to low shear (as it becomes enveloped within a negatively tilted upper trough/low) and moisture.

While development certainly now seems possible, the trick now, is forecasting where it will go. What is expected to help pull this feature north is the advancing frontal trough. For now the system will move towards the northwest, riding the periphery of a quasi-stationary high pressure in the Western Atlantic and by the time the trough arrives, it should be near the western tip of Cuba. However, the 00Z and UKMET have the system much further east, across Cuba and moving east of Florida, then turning west across the state. The remaining model solutions – , and ECWMF has the system in the SE Gulf of Mexico or Florida Straits, remaining west of Florida. Since the system appears further south and east than previously thought, this may satisfy the and UKMET solutions but the consensus is for it to end up in the GOM.

The major impacts of this potential system will be the rain, wind and surf. Regardless of whether the system is or subtropical, the asymmetric rainfall pattern, track and speed implies rainfall totals near 3-5 inches (10-15 cm) across some parts the Florida Peninsula and Panhandle. The tightened pressure gradient between the forecast low and high pressure over the Atlantic implies some possible gale force winds. Please refer to you local weather office.

In summary, there is 50% chance something develops next week with a 30% chance of it being subtropical in nature.

A non tropical low pressure area just east-northeast of Bermuda may also want to transition to subtropical. The latest satellite imagery show bands of cloudiness wrapping and rotating closer to the center as the system remains quasi-stationary. QuikSCAT also showed the gale force winds much closer to the center of this system. In addition, the cyclone has begun to seclude from its associated fronts which implies a feature possibly becoming subtropical. However, cyclone phase diagrams continue to hint this system remains neither warm-core nor cold core and it doesn’t seem to be forecasted to become warm-core. Despite this, the system will continue to be monitored for development.

There are no tropical waves analyzed at this time in the tropical Atlantic or over the mainland of Africa. The first tropical wave that emerged over the waters last week is not being analyzed by the Tropical Prediction center but based on continuation, TPW loops and low level infrared winds, the feature is most likely located near 40W, south of 10N.

Weather456

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Weather456

Edited by Weather456 (Sun May 17 2009 01:23 PM)