Dr. Masters co-founded wunderground in 1995. He flew with the NOAA Hurricane Hunters from 1986-1990. Co-blogging with him: Bob Henson, @bhensonweather
By: Dr. Jeff Masters , 1:17 PM GMT on August 15, 2008
Well, I was right on when I dubbed the tropical disturbance 92L "The Joker" earlier this week. I don't recall ever seeing a system that looked this good on satellite imagery not technically qualify as a tropical depression. Last night's Hurricane Hunter mission did find that 92L had a vigorous circulation at mid levels of the atmosphere, but this circulation did not extend down to the surface. Even when the center of 92L was over northwestern Puerto Rico, I couldn't find any winds out of the west on the island, suggesting that 92L did not have a closed surface circulation. However, the latest QuikSCAT pass from 5:52 am EDT shows that 92L had a large area of west winds south of the island. However, this data was not enough for NHC to upgrade 92L to a tropical depression or tropical storm this morning, presumably because the QuikSCAT data was contaminated by rain and not deemed trustworthy.
Satellite intensity estimates at 2 am and 8am EDT today put 92L at tropical storm strength (40 mph), and visible satellite loops show a well-organized system with a steadily increasing area of heavy thunderstorms. Upper-level outflow is fair on three sides. San Juan, PR radar shows the center of 92L is in the Mona Passage, between Puerto Rico and the Dominican Republic. The rain areas look disorganized, with little evidence of spiral banding. Radar estimated precipitation (Figure 1) shows up to 5 inches of rain has fallen on some regions of the island, with much higher amounts over neighboring ocean areas.
Figure 1. Latest estimated rainfall from 92L.
The forecast for 92L
Wind shear is a mere 1 knot over 92L, as analyzed by the SHIPS model. An upper-level anticyclone has set up on top of 92L, allowing the air lifted from the surface by the storm's heavy thunderstorms to be efficiently spewed out to the sides, ventilating the storm and promoting even more intense thunderstorm activity. This favorable upper-level wind environment is expected to last at least through Sunday. Beyond then, increasing shear may be a problem for the storm.
The latest (2 am EDT) model runs all foresee a track for 92L very close to the north coast of the Dominican Republic and Haiti today through Sunday. Heavy rains will be the main threat to these places, with 4-8 inches likely. Isolated higher amounts of up to 12 inches may fall in the mountains, triggering life-threatening flash floods and mudslides.
In the longer term, an encounter with the rugged terrain of eastern Cuba is forecast by many of the models on Sunday. Passage over the rough terrain of Hispaniola and Cuba could severely disrupt or even destroy 92L. Once the storm finally emerges and stays over the warm waters of the Bahamas or Florida Straits, the models expect it to intensify quickly into a hurricane, possibly a major hurricane. The eventual strength is highly dependent on the track of 92L, with a longer track over water giving it a greater chance of becoming a hurricane. I think the models are overdoing the intensification of 92L once it does pop off the coast of Cuba. We saw in 2006 that Ernesto popped off the coast of Cuba as a weak tropical storm, and took a full 36 hours to get its act together. Still, 92L may have a much longer time over water than Ernesto had, and if the storm does spend 2 or 3 days over the warm waters of the Gulf Stream off the coast of Florida, the storm could easily intensify into a major hurricane, as the GFDL and HWRF models have been predicting for several days now.
The long range track of 92L is highly uncertain. Take your pick of 8 pm/2 am EDT model runs:
GFDL, HWRF: parallel to the east coast of Florida, 50-100 miles offshore, eventually threatening South Carolina
UKMET: Through South Florida
NOGAPS: Through the Florida Keys, into South Florida
ECMWF: Through the Bahamas and into North Carolina
GFS: Through the Bahamas, then west across central Florida in the Gulf of Mexico
Canadian: Across Cuba and through the Cayman Islands, then north in the Gulf of Mexico
No model is calling for "The Joker" to recurve out to sea, completely missing the U.S.
Links to follow
Puerto Rico radar
Wundermap for Puerto Rico
Puerto Rico weather
Elsewhere in the tropics
A tropical wave (93L), near 15N 49W, about 700 miles east of the Lesser Antilles Islands, has gotten better organized this morning. Wind shear has fallen to 10 knots, and is expected to remain below 10 knots the next two days. The system does have a closed circulation at the surface, as seen on last night's QuikSCAT pass. The surface circulation is also apparent on visible satellite loops, as well as a slow increase in heavy thunderstorm activity. NHC has given the reasonable forecast that there is a medium (20-50%) chance that this system will be a tropical depression by Sunday morning. Most of the computer models track this storm well north of the Lesser Antilles Islands, recurving out to sea.
Several of the reliable computer models forecast development of a new tropical wave coming off the coast of Africa about 1-3 days from now.
I'll have an update by 5 pm today, when the latest data from the Hurricane Hunters will be available. "The Joker" is certainly worthy of having a full set of advisories issued for it, given is possible impacts, even if it doesn't technically qualify as a tropical depression. For the future, perhaps NHC should consider an extension to their "Special Tropical Disturbance Statement" that includes a set of forecast tracks, marine forecast, discussion, etc.
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