Leslie bears down on Newfoundland; TD 14 forming

Tropical Storm Leslie has left Bermuda behind, and is chugging north-northeastwards at 18 mph towards an early Tuesday morning encounter with Newfoundland. Leslie brushed by Bermuda on Sunday, with the core of the storm passing 120 miles to the east of the island. The highest winds in Bermuda occurred at Saint David's weather station on the east end of the island, where Leslie brought sustained winds of 39 mph, gusting to 54 mph, at 12:31 pm AST. The station picked up 3.15" of rain from Leslie. A few scattered power outages occurred on Bermuda, but no major damage was reported.


Figure 1. Predicted rainfall from Tropical Storm Leslie, as forecasted by the 2 am EDT September 10, 2012 run of the GFDL model. A large area of 4 - 8 inches of rain (dark green colors) is predicted for western Newfoundland and eastern Nova Scotia. Image credit: Morris Bender, NOAA/GFDL.

Forecast for Leslie
Satellite loops show that Leslie has failed to form an eyewall, and the entire southwest quadrant of the storm is devoid of any heavy thunderstorms. The storm's large size and limited time over warm water will keep it from becoming any stronger than a Category 1 hurricane with 75 mph winds at landfall in Newfoundland near 4 am EDT on Tuesday morning, and it is more likely that Leslie will have top winds just below hurricane strength, 65 - 70 mph. The latest 5 am EDT NHC wind probability forecast calls for a 31% chance that Leslie will be a Category 1 or stronger hurricane Tuesday morning at 2 am EDT, when the storm will be near the coast of Newfoundland. Leslie's strongest winds will be felt on the Avalon Peninsula, on the southeast portion of the island, and the capital of St. Johns will likely experience sustained winds of 45 - 60 mph on Tuesday during the peak of the storm. However, heavy rain will be the main threat from Leslie, and the heaviest rains will fall to the west of the center, where Leslie will be interacting with a cold front. The latest 2 am EDT runs of the GFDL and HWRF models suggest that western Newfoundland and eastern Nova Scotia may receive 4 - 8 inches of rain, which would likely cause moderate to major floods on area rivers.


Figure 2. Tropical Storm Leslie and Hurricane Michael at seen at 9:15 am EDT Monday September 10, 2012. At the time, Leslie had top winds of 60 mph, and Michael was a Category 1 hurricane with 80 mph winds.

Hurricane Michael remains a Category 1 hurricane
The longest-lived hurricane of the 2012 Atlantic hurricane season is Hurricane Michael, which attained hurricane status at 11 pm EDT September 5. Michael remains a Category 1 hurricane with 80 mph winds today, and satellite loops show that Michael is still an impressive storm with a well-developed eye. None of the models show that Michael will threaten any land areas, and Michael will likely weaken below hurricane strength tonight and die at sea over cold waters southeast of Newfoundland in 2 - 3 days.

91L about to become Tropical Depression 14
A tropical wave that emerged off the coast of Africa on Friday (Invest 91L) is about to become Tropical Depression Fourteen, midway between Africa and the Lesser Antilles Islands. Our two most reliable models, the GFS and ECMWF, predict that 91L will pass at least 500 miles to the northeast of the Lesser Antilles Islands late this week, on a track that would likely keep this storm far out at sea away from any land areas.

Elsewhere in the Atlantic
Several of our reliable models predict that the cold front currently sweeping off the U.S. East Coast will leave a trough of low pressure over the ocean near Bermuda late this week, which may serve as the focus for development of a new tropical depression. Any storm that develops in this region would likely have a complicated and difficult-to-predict interaction with 91L (soon to be TD 14), which will pass close to the east.

With today marking the climatological halfway point of the Atlantic hurricane season, the hurricane season of 2012 shows no signs of slowing down from its near-record pace of generating new named storms. Two more tropical waves are predicted to come off the coast of Africa later this week and early next week, and it would not be surprise to see one of these new waves develop by early next week. Today's El Niño discussion from NOAA/CPC shows a continuation of El Niño conditions in the Eastern Pacific, but the atmosphere stubbornly refuses to respond much to the heating of the waters. Wind shear remains seasonably low over the tropical Atlantic Ocean, and is predicted to remain so for at least the next ten days.

Jeff Masters