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The Philippines is making preparations ahead of a powerful Super Typhoon set to strike the island nation Monday morning with effects being felt on Sunday. The storm, known locally as Juan, is feared to have the same flooding potential as Typhoon Ketsana in Sept 2009. Typhoon Megi (a.k.a. Typhoon Juan) has behaved exactly as expected and it is now a very powerful storm designated as Super Typhoon Megi, Super Typhoon Juan or Super Typhoon 15W. Whichever moniker you choose, it is a force to be reckoned with as its energy release compares favorably to an excess of the global electric generating capacity or as an equivalent to the largest yield atomic weapon every minute. Another estimate puts a well developed tropical cyclone energy release on par with 500,000 Hiroshima style atomic bombs per day.

In any event, the inhibiting factors to the storm have gone by the wayside as anticipated and the central pressure has dropped to 908 mb, which is extremely low. To provide a frame of reference of how that compares to intense hurricanes in the North Atlantic, Hurricane Camille in 1969 bottomed out at 909 mb and had winds approaching 200 mph. Hurricane Andrew in 1992 had a minima pressure of 922 mb and the lowest that Katrina had in 2005, well before landfall, was 920 mb. Super Typhoon Megi is not too far from the all-time lowest recorded atmospheric pressure which occured in 1979 with Typhoon Tip, which had a remarkable central pressure of 870 mb. Previously, Typhoon Ida held the record of 879 mb when it was 750 miles east of Luzon (very close to the current location of Megi-450 miles NE of Manila) in 1958. So, extremely intense storms in the region are not totally uncommon. The clouds that had been obscuring the center have gone by the way-side and a well defined, relatively small eye has developed.

A pressure approaching 900 mb can easily support higher winds than the 3 UTC (Z) Oct 17 2010 analysis of 140 kt sustained winds of 140 kts and gusts to 170 kts, which translates to sustained winds of 161 mph or 259 kph and gusts to 195 mph or 315 kph. Some further intensification is possible as the forecast calls for sustained winds to increase to 145 kts and gusts to 175 kts. While the pressure can support even higher winds than that, at this point, they are so strong that it almost becomes academic in relation to the destruction potential and the ultimate intensity at landfall will most likely be subject to eyewall replacement cycles. When a tropical cyclone goes through an eyewall replacement cycle, central winds typically fall off but the breadth of gale force winds expands. That was the case with Hurricane Katrina which “only” had winds of 125 mph at landfall as it headed into Mississippi but 100 mph winds were felt all the way to Mobile. Another factor that may inhibit substantial intensification would be a slight disruption of the northern outflow. This is an example of why it is difficult for an extremely intense tropical cyclone to maintain its maxima for long as environmental conditions must be perfect and perfect conditions rarely last long. Nevertheless, as it stands, the official forecast from the Joint Typhoon Warning Center puts the winds around 140 kts at landfall sometime after 00 UTC (Z) October 18, 2010 north of Palanan and east of Tuguegarao. It would not be out of the question for winds to exceed forecast levels at some point in time. The timing of eyewall replacement cycles, however, is beyond current forecast abilities until the beginning of the cycle change is actually observed.

As was anticipated, the trof of low pressure near Okinawa that was causing a weakness in the steering ridge to the North has moved northeast and the ridge filled in. Consequently, the previous west northwest track of Megi has shifted westward at 12 kts. The ridge is expected to continue to build such that the westward track should change around the time that the storm gets to the coast of Luzon such that it moves west-southwest. That track would take Megi over the mountainous regions of northern Luzon but well north of Manila. The storm surge on the eastern, northeastern and northern part of the island will be extreme but exact levels will be determined by the geogrpahy of the coast. The mountains will enhance the rain totals which will most likely be extreme. Even as it loses intensity rapidly over the mountains, the circulation will be such that there will be an onshore flow off of the South China Sea toward Manila for a period of time so rain totals will most likely be high on both sides of Luzon.

If there is any good news to report it is that the forward speed may increase a bit and so the center of the storm may be over Luzon for only about 12 hours. That’s plenty of time to do plenty of damage but at least its not going to crawl across the Philippines and extend the high risk for catastrophic flooding. By 12UTC (Z) October 18, 2010 Typhoon Megi should re-emerge over the ocean in the South China Sea with winds forecast to have been reduced to 95 kts. However, once over the warm waters of the ocean, Typhoon Megi will regain some strength but most likely will not get back to it’s former self…that would be extremely rare and there simply will not be time nor will the environmental conditions support such a scenario. Even so, It is expected to get back to 115 kt sustained winds by 00UTC (Z) October 22, 2010.

Previously, the extended forecast track had suggested a second landfall on the South China island of Hainan followed by a final landfall after crossing the Gulf of Tonkin in Vietnam. Modeling data though has formed a consensus though of another trof coming down through Asia.

That trofiness is expected to influence Megi northwest after it enters the South China Sea. The depth of that trof will determine the fate of Megi. If it is slow or not so strong, then Megi may run into China south of Hong Kong, though it would still be close enough to affect that city. If the trof is a little deeper, then it could turn Megi for a more direct affect on Hong Kong and if the trof is fast and very deep, it could conceivably turn the storm north and then northeast. While there may not be sufficient room in the sea for this to occur without striking land, that scenario would put Taiwan at risk of a hit from the Southwest and potentially even Japan after that. It’s way too soon to tell. One thing seems invevitable: the Northern Philippines will be affected adversely of the effects of a major tropical cyclone by 00UTC (Z) 18 October 2010.