Franklin Continues, Waves Across the Atlantic

The Following Discussion was issued by Rob & Jason (and a tip of the cap to our budd, Kevin) over at IWIC...sums up the current situation pretty well:

"IWIC Worldwide Tropical Weather Discussion - July 28 2005 - 22:00 UTC

Tropical Storm Franklin has made a bit of a comeback today. Convection has flared a bit closer to the center and the cloud pattern has become slightly better organized. An additional 5-10KT increase in strength is very possible before the storm becomes carried northward by an upper trough. On this projected track, the storm should stay well offshore the US east coast.

A large-amplitude tropical wave, INVEST 92L, and associated broad 1013MB low is approaching 50ºW. The low is currently positioned on the southern end of the wave axis, however visible imagery depicts greater low-level curvature further north. Furthermore, dry Saharan Air is still wrapped within the wave, particularly on the northern side, which is keeping convective flare-ups to a minimum. Thus, the system still needs to consolidate more and enter a more unstable environment before development becomes an imminent concern. Having said this, conditions become increasingly more favorable closer to the Windward islands and all the way to the Bahamas. Oceanic heat content is high, coinciding with unseasonably warm sea-surface temperatures. Upper-level wind shear is on the low side, with the core westerly winds from the subtropical jet remaining well to the north. In fact, the latest CIMSS GOES-12 analysis indicates ridging is slowly increasing aloft the wave. Moreover, the influence of the Saharan Air Layer is lessening as it progresses further west. All of this data suggests that while the wave is far from being a classified tropical cyclone, further organization and increasing convection seems likely over the next few days. Given the extent of the environmental favorability where 92L is headed, a tropical depression cannot be ruled out within the next 48-60 hours.

INVEST 92L is moving generally west-northwestward. Global model guidance is rather converged on the projected track. The 12Z NOGAPS, UKMET, CMC, and ECMWF plus 18Z GFS all show a continued west-northwest motion through or just north of the Leeward Islands over the next 48 hours and then passing in the vicinity of the Bahamas by the end of the forecast period. Once near the Bahamas on Day Six, models vary on the precise alignment and strength of the ridge weakness over the eastern US and the ridge itself. The ECMWF, usually a reasonable medium-range model, takes the system all the way into the Gulf of Mexico by the middle of next week. Although it is somewhat of an outlier and no other model seems to show as intense of a ridge as the ECMWF depicts, it is worth noting the strong right bias in the model consensus for storms in this area during 2004 and early this season. The GFS slows it down in the Bahamas under supposedly collapsed steering currents, similar to what recently took place with Franklin the same area earlier last week, whereas the others show what seems to be a straight shot to somewhere along the southeast US coast beyond the runs' time frames. Development from this area is not a certainty, though the chance is very much there. IF this does consolidate and become a tropical cyclone, conditions should favor quicker intensification once in the Bahamas and we could be faced with a hurricane threat. "If" is the key word.

Behind INVEST 92L, another tropical wave and mid-level center is noted, dubbed INVEST 93L. This system looked very well organized for a brief time late last night but has since become weaker. First off, the wave is not high-amplitude like the one discussed above, thus making it more susceptible to unfavorable conditions. Convection is sporadic in nature and there are no signs of either a surface low or a ridge aloft. Although sea surface temperatures are warm, this system is experiencing increased shear from the upper-level anticyclone to the west. As this ridge continues to build aloft 92L, this hinderance may only worsen with time. Furthermore, 93L is under moderate Saharan Air Layer influence from the north and east. Global models are not aggressive on developing the storm; none show anything more than a weak low in the shadows of a stronger system over the next six days. It is possible that some slow development could occur once and if the system can achieve a low-level circulation, though even so, anything significant seems unlikely. The future track is a moot point given the low prospects, but if a storm were to develop it would likely follow west-northwestward on the heels of the wave discussed above.

Yet another area of convection has emerged off the coast of Africa, behind both aformentioned INVESTs. This has not yet been identified in association with a tropical wave, but is rather a result of the intertropical convergence zone. Today's runs of the GFS and NOGAPS indicate this will become a tropical cyclone in the forecast period as it too moves west-northwestward. No other model has yet shown any significant development, so there is not a convincing consensus at this time. One plus for this system is that it is at a relatively low latitude, which may prevent it from experiencing the core of the Saharan Air Layer. Since conditions are apparently not that unfavorable, this system will be monitored as it traverses the tropical Atlantic.

Some global models are hinting at increased low-level vorticity in the northern Gulf of Mexico on the tail end of a trough split in the next 4-5 days. None develop a true tropical cyclone, and any low that does form would probably have to work hard to make it to the surface, not to mention it would be a primarily baroclinic origination. This will too be watched, though nothing is expected at this time."

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2005 Forecast: 14/7/4

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