Jeff co-founded the Weather Underground in 1995 while working on his Ph.D. He flew with the NOAA Hurricane Hunters from 1986-1990.
By: Dr. Jeff Masters , 18. lokakuuta 2010 klo 13:23 (GMT)
Super Typhoon Megi hit northern Luzon Island in the Philippines near 3:30 UTC this morning as a Category 5 Super Typhoon with sustained winds of 165 mph and a central pressure of 914 mb, as rated by the Navy Research Lab in Monterey. Megi is the strongest Category 5 tropical cyclone to make landfall in the world since August 21 2007, when Hurricane Dean hit Mexico's Yucatan Peninsula with sustained winds of 175 mph and central pressure of 905 mb. We were fortunate to get precise measurements of Megi's intensity yesterday morning thanks to the Hurricane Hunters, who were investigating the typhoon in support of the Interaction of Typhoon and Ocean Project (ITOP), which is studying how the ocean responds to typhoon growth and movement in the Western Pacific Ocean. A C-130 hurricane hunter aircraft penetrated into Megi at 10,000 feet, and found an extraordinarily intense storm. At 9:05am EDT on Sunday (13:09 UTC), the aircraft recorded a central pressure in Megi of 890 mb. This is a phenomenally low pressure, ranking Megi (unofficially) as the 16th strongest tropical cyclone in world history. Only two Atlantic hurricane have been more intense than Megi--Wilma (2005) at 882 mb, and Gilbert (1988) at 888 mb. As they penetrated Megi's eyewall, the Hurricane Hunters performed the standard practice of maintaining a constant "pressure altitude"--the altitude one would expect to find a 700 mb pressure at in an atmosphere at standard conditions. In order to maintain a constant pressure altitude of 10,000 feet, the aircraft was forced to descend 3,000 feet in altitude as it entered Megi's eye. The aircraft entered the eye at 7,000 feet, so the pressure in Megi's eye was what one would normally find at an altitude 3,000 feet higher in the atmosphere. The aircraft recorded a remarkable increase in temperature of 12°C (22°F) as it crossed from the eyewall into the warm eye of Megi. A 12°C rise in eye temperature is extraordinarily rare in a tropical cyclone. Equally noteworthy were Megi's winds. The Hurricane Hunters measured winds at flight level of 220 mph, which normally translates to a surface wind speed of 198 mph, using the standard 10% reduction. The SFMR surface wind measurement instrument recorded surface winds of 186 mph in regions where heavy rain was not contaminating the measurement, but found surface winds of 199 mph in one region of heavy rain. Now, this measurement is considered contaminated by rain, but at very high wind speeds, the contamination effect is less important than at lower hurricane wind speeds, and it is possible than Megi's surface winds reached sustained speeds of 200 mph. However, data from a dropsonde in the eyewall at the time supported giving Megi just 180 mph sustained winds. This is still a ridiculously strong wind, equivalent to a violent EF-4 tornado on the Enhanced Fujita Scale.
Figure 1. Visible satellite image of Megi taken by NASA's Terra satellite at 2:25 UTC October 18, 2010. Image credit: NASA.
Passage over Luzon Island has weakened Megi to a still-formidable Category 3 typhoon with 125 mph winds, and Megi is pounding the northern portion of the island with torrential rains. We don't have many cities in the Philippines along Megi's path that report weather conditions, so it is difficult to know how strong the storm is. Tuguegarao, to the north of where Megi's eyewall passed, bottomed out at 978 mb pressure, had top sustained winds of 27 mph, and picked up 3.23" of rain thus far from the storm. Megi's rains, which will likely accumulate to more than a foot along a wide swath of northern Luzon (Figure 2), will create dangerous mudslides and life-threatening flash floods. Once Megi crosses Luzon, the storm is expected to re-intensify and hit the Chinese coast between Hainan Island and Hong Kong as a major typhoon on Friday.
Figure 2. Rainfall forecast for the 24 hours ending at 8pm EDT October 18, 2010, based on satellite estimates of Megi's rainfall rate. Rainfall amounts in excess of 12 inches (red colors) were predicted along a wide swath of Luzon Island. Image credit: NOAA/NESDIS.
Caribbean disturbance 99L
Heavy thunderstorm activity has increased over the past day over the southwestern Caribbean off the coasts of Nicaragua and Honduras in association with a tropical disturbance (Invest 99L). Recent satellite imagery does show this disturbance has some rotation, and wind shear is a moderate 10 - 20 knots, which is low enough to allow some slow development. However, the disturbance is headed west-northwest at 5 - 10 mph, and most of the computer models predict the storm will move over Nicaragua on Tuesday, which would not give 99L enough time over water to develop into a tropical depression. NHC is giving 99L a 30% chance of developing into a tropical depression by Tuesday. The storm will bring very heavy rains of 3 - 6" to northern Honduras and northeast Nicaragua over the next two days.
I'll have an update Tuesday morning.
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