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Tropical Storm Richard slowly intensifying

By: Dr. Jeff Masters, 7:31 PM GMT on October 21, 2010

Tropical Storm Richard is here, the seventeenth named storm of this very busy 2010 Atlantic hurricane season. Richard's formation puts 2010 in 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.

We won't have another hurricane hunter aircraft in Richard until 8pm tonight, so we will have to rely on satellite intensity estimates until then. The closest buoy to Richard is NOAA buoy 42057, which is on Richard's weak side about 100 miles from the heaviest thunderstorms. Winds at the buoy were just 18 mph, gusting to 22 mph, at 2:43pm EDT this afternoon. Recent satellite imagery shows that Richard is steadily organizing, with several curved spiral bands forming on the storm's south and east sides. The storm is bringing very heavy rain to Jamaica. Water vapor satellite loops show considerable dry air to the west and north of Richard, and the southwesterly upper-level winds over the storm are bringing some of this dry into the core of the storm, keeping all the heavy thunderstorm development confined to the east side of the center. The waters beneath Richard are very warm, 29°C, and Richard will begin taking advantage of these warm waters now that the shear is falling.

Figure 1. Afternoon satellite image of Richard.

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, through Monday morning. As the storm moves westwards on Friday, it will position itself beneath an upper-level high pressure system, which will aid the storm's upper-level outflow. With water temperatures a very warm 29°C and warm waters extending to great depth, Richard should be able to attain at least Category 1 hurricane strength by Saturday. NHC is currently giving Richard a 11% chance of becoming a major Category 3+ hurricane. I believe the odds are higher, near 30%. 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 steadily weaken.

Track forecast for Richard
The latest set of 8am EDT (12Z) model runs are similar to the previous set of runs, and don't help illuminate what the long-range fate of Richard might be. Steering currents are weak in the Western Caribbean, and will remain weak through Friday morning, resulting in a slow, erratic movement for Richard. Most of the models favor a southerly, then southwesterly path at 5mph or less over the next two days. This may bring the center of Richard very close to or over the northern coast of Honduras on Saturday or Sunday, as predicted by the GFS, UKMET, and NOGAPS models. These models then show Richard dissipating over Central America. A much different solution is offered by the ECMWF, HWRF and GFDL models, which foresee less of a southerly motion for Richard over the next two days, resulting in the storm missing the north coast of Honduras by one hundred miles or more. These models take Richard to the northwest across the tip of the Yucatan (GFDL and ECMWF models) or western tip of Cuba (HWRF model) on Sunday or Monday. The HWRF and GFDL models predict Richard will be a threat to the west coast of Florida on Tuesday. NHC takes the reasonable approach of predicting a path somewhere between these two extremes, with Richard crossing the Yucatan between Cozumel and the Belize/Mexico border. Residents of northern Honduras should anticipate the possibility that Richard will pass very close or strike Honduras on Saturday or Sunday. Very heavy rains of 4 - 8 inches are possible over the the weekend in coastal Honduras beginning Friday night or Saturday morning. The 11am EDT NHC wind probability forecast is giving the highest odds for tropical storm-force winds at Guanaja in Honduras, at 46%. Cozumel, Mexico is given a 42% chance, Key West a 6% chance, and Ft. Myers a 3% chance.

Invest 90L
A tropical wave that emerged off the coast of Africa yesterday (Invest 90L) has a modest amount of spin and some growing thunderstorm activity. Wind shear is a moderate 5 - 15 knots, and the waters are still warm enough to support tropical storm formation. NHC is giving the system a 30% chance of developing into a tropical depression by Saturday. By Sunday, 90L will encounter 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.

Typhoon Megi takes aim at China
Typhoon Megi continues it slow march towards China at 5 mph, and is expected to make landfall Saturday morning on the Chinese coast opposite from Taiwan. Megi has maintained strength as a Category 3 typhoon with 115 mph winds today, despite rising wind shear (now a moderate 10 - 20 knots) and cooling sea surface temperatures. Megi is moving slow enough and is large and powerful enough that it is probably upwelling cold water from the depths to the surface faster than it can move away, and these upwelling cool waters are keeping Megi from being a stronger storm. Wind shear will increase dramatically to 20 - 40 knots on Friday as the typhoon makes its final approach to the coast of China, and this shear should be high enough to reduce Megi to Category 1 status before landfall. Megi will still be a very large and powerful storm capable of causing considerable wind and storm surge damage even at Category 1 strength. However, heavy rain will likely be the storm's main threat, since it 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 are already affecting the coast of China near Taiwan, as seen on China's radar composite, as well as Taiwan radar.

The clean-up continues in the Philippines from Megi, which hit northern Luzon island on Monday morning at 3:30 UTC as a Category 5 super typhoon with sustained winds of 165 mph and a central pressure of 914 mb. Severe damage was done to Isabela Province in northern Luzon, and 19 deaths are being blamed on the storm. Considering most major typhoon that have hit the Philippine in recent year have killed hundreds and sometimes thousands of people, the low death toll from Megi is a testament to the excellent efforts by officials in the Philippines to get people out of harm's way in advance of the storm.

Figure 2. Rainfall rate for Megi as observed by the TRMM polar orbiting satellite at 10:01am EDT October 21, 2010. Heavy rains in excess of 0.8" per hour (yellow colors) were present in Megi's eyewall and spiral bands. Image credit: Navy Research Lab, Monterey.

Next update
I'll have an update Friday morning.

Jeff Masters


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