Major steering current shift; Typhoon Man-Yi wallops Okinawa

There are no threat areas in the tropical Atlantic to discuss, and none of the computer models are forecasting tropical storm formation over the coming week. However, there is there a major development to report--it appears likely that a major shift in the weather pattern will occur in late July across the Northern Hemisphere. If the GFS model is correct, the trough of low pressure that has been consistently in place over the Eastern U.S. will finally move off, to be replaced by a ridge of high pressure (Figure 1). This would bring a hurricane steering pattern much like we saw in 2004 and 2005, with increased risk for the Gulf of Mexico and reduced risk for the U.S. East Coast from the Carolinas northward. The east coast of Florida would remain at normal risk. The GFS model has been inconsistent in its prediction of the timing of this shift, but has been persistent enough about it that I'm forecasting a 70% likelihood of this major pattern shift occurring by the end of July. Such a shift would bring the western U.S. some relief from the current heat wave, and bring high heat and air pollution problems to the Midwest and East Coast. How long such a shift might last is impossible to predict--it could last for a week, or could remain in place for the remainder of hurricane season. I'll have an updated forecast on this pattern shift Monday, when I issue my bi-weekly hurricane outlook.



Figure 1. Observed 500 mb heights at 00 GMT today (top), and forecast height in two weeks' time from the GFS model(bottom). The white lines in these plots show how close to the surface a pressure of 500 millibars (mb) is found. When there is low pressure aloft, due to a trough of low pressure, the height at which a pressure of 500 millibars is found moves closer to the surface, and one sees a "U" shaped area of 500 mb height lines. We can see a trough over the Eastern U.S. in the top plot. When a ridge of high pressure occurs aloft, the height at which a pressure of 500 millibars is found moves higher up in the atmosphere, away from the surface, and one sees an upside-down "U" shape to the height lines. A ridge of high pressure is apparent over the Eastern U.S. in the bottom plot. This ridge of high pressure over the Eastern U.S. will be accompanied by an extension of the Bermuda High to the west over the the U.S., which will act to block recurvature of hurricanes.

Typhoon Man-Yi
In the Pacific, Typhoon Man-Yi battered Japan's Okinawa Island this morning, striking as a super typhoon with 155 mph winds. Naha, Okinawa recorded sustained winds of 76 mph with gusts to 105 mph (Figure 1), and a pressure of 939 mb. This was very close the the minimum pressure estimated by satellite, 937 mb. Media reports indicate substantial damage occurred on Okinawa, and over 100,000 people lost power. Twelve crew members of a Chinese ship were missing after the vessel sank some 600 km northwest of Guam in strong winds and high seas. Man-Yi is expected to make landfall on the Japanese island of Kyushu Saturday. However, the storm should weaken to a Category 1 storm by landfall, as wind shear from an approaching trough of low pressure has already reached 20 knots on the west side of the storm, and is expected to increase further. Some links for those following the storm:

Japanese radar. Click on an area of interest to zoom in.

Latest satellite images of Typhoon Man-Yi, courtesy of NOAA.

Guam sector satellite images.

Awesome image of Man-Yi from NASA's Aqua satellite.

Current conditions in Japan:
Kagoshima, southern Japan
Miyazaki, southern Japan
Tanegashima, southern Japan


Figure 2. Wind trace from Okinawa airport during Typhoon Man-Yi. Note the shift in wind direction as the eye passed over, and sharp drop in wind speed at this time.

Jeff Masters