WunderBlog Archive » Category 6™

Category 6 has moved! See the latest from Dr. Jeff Masters and Bob Henson here.

Richard not strengthening yet; Category 4 Giri hits Myanmar; Megi approaching China

By: Dr. Jeff Masters, 2:04 PM GMT on October 22, 2010

Tropical Storm Richard remains a minimal strength tropical storm this morning, but is poised to begin a period of steady intensification that should take it to hurricane strength by Sunday. Richard is the seventeenth named storm of this very busy 2010 Atlantic hurricane season, putting 2010 into 6th place for the greatest number of named storms in the Atlantic since record keeping began in 1851. Only 2005 (28 named storms), 1933 (21 named storms), 1995 (19 named storms), 1887 (19 named storms), and 1969 (18 named storms) had more.

An Air Force hurricane hunter aircraft is currently in Richard, but has not seen much change in the storm's winds. As of 9:45am EDT this morning, top winds at flight level of 1200 feet were 46 mph, and the top surface winds seen so far by their SFMR instrument were 49 mph. The closest buoy to Richard is NOAA buoy 42057, which is on Richard's weak side about 80 miles northwest of the center. Winds at the buoy were 34 mph, gusting to 43 mph, at 8:44am EDT. Recent satellite imagery shows that Richard has become more organized since last night, with a large Central Dense Overcast (CDO) of high cirrus clouds forming over the center. A CDO is created when strong thunderstorms near the center of a developing tropical storm create updrafts that shoot moisture high into the atmosphere. When the moisture hits the bottom of the stratosphere, the moisture condenses into cirrus clouds that flatten out and spread horizontally into the CDO, which is kind of like a giant version of the flat anvil top one sees at the top of mature thunderstorms. The low-level center of Richard is no longer nearly exposed to view, and heavy thunderstorms are now firing off near the center, a sign that wind shear has relaxed and serious intensification can progress. Richard has several curved spiral bands forming on the south and east sides, and upper level outflow is improving on all sides except the west. Satellite intensity estimates put Richard's strength at about 50 - 55 mph. Water vapor satellite loops show considerable dry air to the west of Richard, and this dry air may cause some trouble for the storm over the next few days. The waters beneath Richard are very warm, 29°C.

Figure 1. Total accumulated rainfall for Richard predicted by the 2am EDT (6Z) October 22, 2010 run of the GFDL model. The model expects top rains from Richard in the 4 - 8 inch rain (dark green colors) with a few isolated areas of 8+ inches. Image credit: Morris Bender, NOAA/GFDL.

Intensity forecast for Richard
The latest SHIPS model forecast predicts that wind shear over the Western Caribbean will remain in the low range, 5 - 10 knots, today through Tuesday. As the storm moves westwards on Saturday, it may draw close enough to coast of Honduras to hamper intensification. Assuming Richard avoids making landfall in Honduras, the light shear and warm waters that extend to great depth should allow Richard to intensify into a Category 1 hurricane by Sunday. The 5am NHC wind probability forecast is giving Richard a 4% chance of becoming a major Category 3+ hurricane. I believe the odds are higher, near 20%. The main inhibiting factor for intensification will be interaction with the north coast of Honduras, and the possibility of the dry air to the west of Richard getting wrapped into the core of the storm while it is trying to organize. A band of very strong upper-level winds associated with the jet stream will be over the Gulf of Mexico early next week, so it is likely that if Richard crosses into the Gulf of Mexico, the storm will be unable to intensify once it passes north of the latitude of the Florida Keys.

Track forecast for Richard
The latest set of 2am EDT (6Z) model runs are in much better agreement on the path of Richard compared to yesterday. Steering currents are weak in the Western Caribbean, and Richard will move little today. By Saturday, Richard will begin moving due west in response to a ridge of high pressure that is expected to build in over the Caribbean. This path will bring the center of Richard close to the northern coast of Honduras on Saturday and Sunday, resulting in very heavy rains of 3 - 7 inches along the coast. None of the models predict a more northwesterly path towards Cancun/Cozumel or the western tip of Cuba any longer, and Florida is not at risk of Richard coming its way over the next five days. The 5am EDT NHC wind probability forecast is giving the highest odds for tropical storm-force winds at Guanaja in Honduras, at 54%. Belize City is next highest, at 42%, and the odds have dropped to 28% for Cozumel. If Richard never reaches hurricane strength, it may dissipate over the Yucatan Peninsula, as predicted by the NOGAPS, GFS, and ECMWF models. If Richard does intensify into a hurricane, as predicted by the GFDL model, the storm may survive crossing the Yucatan, and emerge into the Gulf of Mexico on Tuesday. Very high wind shear associated with the jet stream is expected to be over the Gulf of Mexico next week, so if Richard begins moving north or northeast towards the U.S. Gulf Coast, steady weakening is to be expected.

Invest 90L
A tropical wave (Invest 90L) about 100 miles south of the Cape Verde Islands off the coast of Africa has a modest amount of spin and heavy thunderstorm activity. Wind shear is a moderate 10 - 20 knots, and the waters are warm enough to support tropical storm formation. NHC is giving the system a 30% chance of developing into a tropical depression by Sunday. By Sunday, 90L's northwest movement will take the storm into a region of high wind shear of 20 - 40 knots, discouraging further development. This system is not a threat to cross the Atlantic and affect the Lesser Antilles or North America.

Cyclone Giri hits Myanmar
Powerful Cyclone Giri is making landfall this morning on the coast of Myanmar (Burma) as a Category 4 storm with 145 mph winds. Giri is one of the strongest cyclones ever to hit Myanmar, and has winds 10 mph stronger than Cyclone Nargis of 2008, which killed over 138,000 people. However, Giri is hitting a portion of the Myanmar coast that is not low-lying, and the major threat from Giri will be wind damage and flooding from heavy rains. Giri put on an impressive rapid intensification burst over the past 18 hours, strengthening from a 60 mph tropical storm at 8am EDT yesterday to a 145 mph Category 4 storm by 2am this morning.

Figure 2. Visible MODIS satellite image of Tropical Cyclone Giri taken at 2:55am EDT October 22, 2010. At the time, Giri was a Category 4 storm with 145 mph winds. Image credit: NASA.

Typhoon Megi unleashes torrential rains on Taiwan and China
Torrential rains from Typhoon Megi have triggered flooding and landslides in Taiwan that have left 3 people dead and more than 20 missing. The typhoon is also being blamed for the deaths of 36 people and $176 million in damage earlier this week in the Philippines. Megi continues its slow march towards China at 5 mph, and is expected to make landfall Saturday morning on the Chinese coast opposite from Taiwan. Megi remains a large and powerful Category 2 typhoon with 110 mph winds today, but rising wind shear is beginning to erode the northern portion of the storm's eyewall. It likely that Megi's eyewall will collapse before landfall, resulting in substantial weakening to a Category 1 storm. Megi will still be a very large and powerful storm capable of causing considerable wind and storm surge damage even at Category 1 strength. Heavy rain will likely cause serious flooding since Megi is moving slowly and is a huge storm. I expect Megi will be a billion-dollar disaster for China, mostly due to flooding from heavy rains. The outer rain bands of Megi will affect Taiwan and the coast of China near Taiwan all day today, as seen on China's radar composite and Taiwan radar.

Figure 3. Radar image of Typhoon Megi at 8:20am EDT (20:20 Taiwan time) on October 22, 2010. Image credit: Taiwan Central Weather Bureau.

Next update
I'll have an update this afternoon.

Jeff Masters


The views of the author are his/her own and do not necessarily represent the position of The Weather Company or its parent, IBM.