Ophelia strengthening; Typhoon Nalgae a new threat to the Philippines

Tropical Storm Ophelia is strengthening as it pulls away from the Lesser Antilles Islands and heads north-northwest. Recent satellite loops show that Ophelia has developed a Central Dense Overcast (CDO) of high cirrus clouds over its core, which is characteristic of strengthening tropical storms that are nearing hurricane intensity. Dry air and moderate wind shear of 15 - 20 knots are slowing down Ophelia's intensification, but by Friday morning, wind shear is expected to fall to 10 - 15 knots, and remain below 15 knots through Sunday morning. This should allow Ophelia to intensify into a hurricane on Friday. Most of the models agree that Ophelia will track far enough to the east of Bermuda that the island should see sustained winds below 45 mph, since it will be on the weak (left) side of the storm. We can't rule out the possibility that Bermuda will receive hurricane force winds yet, but the odds are low--the 5 am wind probability forecast from NHC gave Bermuda just a 3% chance of receiving hurricane force winds. Ophelia's closest approach to the island will be late Saturday night and early Sunday morning. Ophelia is likely to bring high winds and heavy rains to Southeast Newfoundland Sunday night, as a weakening tropical storm.

In the middle Atlantic, Tropical Storm Philippe is headed west-northwest, and is not expected to trouble and land areas. Satellite loops show Philippe is a small system with little heavy thunderstorm activity. Wind shear is expected to diminish some today over the storm, which should allow the storm to intensify. However, by Saturday, Philippe will be encountering very high wind shear of 30 - 40 knots associated with the upper-level outflow from Ophelia. This shear will probably be high enough to destroy Philippe by Monday. In the event Philippe does survive the shear, the storm could penetrate far enough west that Bermuda might need to be concerned with it.

Elsewhere in the Atlantic, none of the computer models is calling for a new tropical storm to form in the coming seven days. The large-scale environment over the Atlantic currently favors sinking air, due to the current phase of the Madden-Julian Oscillation (MJO). This situation will likely last well into next week, and will discourage formation of new tropical storms. The MJO is a 30-60 day cycle of thunderstorm activity that affects the tropics.


Figure 1. Morning satellite image of Ophelia, showing the large Central Dense Overcast (CDO) that has formed.

Typhoon Nesat battering China
Typhoon Nesat hit China's Hainan Island today as a Category 1 typhoon with 75 mph winds. While Nesat's winds and storm surge will not cause major damage, it is a very wet storm, capable of dropping up to 8 inches of rain in 24 hours, according to latest satellite rainfall forecasts. Haikou on Hainan Island recorded a wind gust of 78 mph and 3.23" of rain as the eyewall passed just to the north. Nesat will hit Vietnam near Hanoi as a tropical storm on Saturday.

Nesat roared across Luzon Island in the Philippines Monday as a powerful Category 3 typhoon with 120 mph winds, leaving 35 people dead and 45 missing. The Philippines has a new worry today: Typhoon Nalgae has formed 700 miles to the east of Luzon Island, and is expected to follow a course just to the north of Nesat's. Nalgae is expected to intensify into a major Category 3 typhoon and hit the northern portion of Luzon on Saturday afternoon, local time. With soils on the island already saturated from the heavy rains Nesat brought, the new typhoon promises to bring heavy flooding to Luzon this weekend.


Figure 2. True-color MODIS image of Typhoon Nesat over the South China Sea taken at 1:35 pm local time September 28, 2011. At the time, Nesat was a Category 1 typhoon with 75 mph winds. Image credit: NASA.

Jeff Masters