Ophelia, wave nearing Windward Islands, and blob near Puerto Rico

Wave nearing Windward Islands
A well-organized tropical wave 850 miles east of the Windward Islands has not improved in organization this afternoon, but still has the potential to develop into Tropical Depression 17 in the next few days. The wave has a decent surface circulation visible on satellite imagery and QuikSCAT satellite measurements, but deep convection is limited. The wave, located near 9N 48W, is suffering from being too far south and from 10 - 15 knots of wind shear. The disturbance is expected to continue moving west-northwest at 10-15 mph the next few days into a region with less shear. The upper level environment is favorable--an anticyclone has formed on top of it, which should provide very favorable outflow for any deep convection that fires up.


Figure 1. Early track model runs for the disturbance that may turn into Tropical Depression 17.

Blob north of Puerto Rico
A pronounced area of thunderstorms has developed north of Puerto Rico this afternoon, in the base of a large trough of low pressure over the Atlantic. This disturbed area lies in an area of uniform easterly winds that will blow the thunderstorms to the west towards Cuba and the Bahamas. Upper level wind shear is currently high over the disturbance--about 20 knots--but is expected to drop once the disturbance reaches the Bahama Islands on Saturday or Sunday. A tropical depression could form then or early next week when the disturbance crosses into the Gulf of Mexico.

Shear values in general over most of the Gulf of Mexico and Caribbean are expected to drop to very low levels favorable for tropical development during the next week, and I think it is likely that we will see a tropical storm in either the Gulf or Caribbean then.

Ophelia
I'm trying to imagine a day when I don't talk about Ophelia moving slowly, but today is not the day. Perhaps tomorrow; the next trough swinging off the East Coast should be able to pick her up and move her out late in the day.

Ophelia is a shell of her former self. The eyewall has disintegrated, and the latest SFMR wind data from the NOAA hurricane hunters shows just a very small area of hurricane force winds over the water. Cooler waters, dry air, and wind shear are all taking their toll on Ophelia, and by the time she races past Cape Cod on Saturday, the worst she will be able to do there is generate wind gusts of 40 mph.


Figure 2. Winds in Ophelia at 12:30pm EDT today measured by the NOAA hurricane hunters.

Storm surge levels observed last night in Bogue Sound, which is the bay between Morehead City and its barrier island, reached seven feet--near the record levels set there from Category 3 Hurricane Hazel in 1954. The storm surge reached 10 feet in some of the smaller creeks in the Neuse River and may have reached 12 feet, a remarkably high storm surge for what was a tropical storm for that area. High storm surges can result from just tropical storm force winds, if they blow over a large area for a really long time, like Ophelia's did.


Figure 3. Storm Surge heights measured in Ophelia.

For those of you who can handle a 1.6Mb animation, the radar loop from Morehead City, NC during the time Ophelia's northern eyewall passed over the city is fascinating. The turbulence created by having part of the eyewall over land and part over water created some smaller vorticies along the inside edge of the eyewall.

While Ophelia did dump it share of heavy rain--around 5 - 7 inches near Wilmington, and over 10 inches around Cape Fear, south of Wilmington--the rain was mostly confined to the coast, and did not cause widespread flooding problems. Ophelia's winds also did relatively light damage--sustained hurricane force winds (74 mph) were only observed at one location, on Cape Lookout near the Outer Banks. The storm surge was what caused the main havoc with Ophelia.


Figure 4. Estimated rainfall from the Morehead City radar for Ophelia's passage.

Jeff Masters