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 , 2:47 PM GMT on September 17, 2010
Hurricane Karl explosively deepened into a dangerous Category 3 hurricane this morning, becoming the fifth major hurricane of this remarkably active 2010 Atlantic hurricane season. Karl is the first major hurricane on record in the Gulf of Mexico's Bay of Campeche--the region bounded by the Yucatan Peninsula on the east. There were two other major hurricanes that grazed the northern edge of the Bay of Campeche, Hurricane Hilda of 1955 and Hurricane Charley of 1951, but Karl is by far the farthest south a major hurricane has been in the Gulf of Mexico. Hurricane records go back to 1851, but Karl is a small storm and could have gotten missed as being a major hurricane before the age of aircraft reconnaissance (1945).
Figure 1. Tracks of all major hurricanes since 1851 near Mexico's Bay of Campeche. Karl is most southerly major hurricane on record in the Gulf of Mexico. Image credit: NOAA Coastal Services Center.
With Karl's ascension to major hurricane status, we are now ahead of the pace of the terrible hurricane seasons of 2004 and 2005 for number of major hurricanes so early in the year. In 2005, the fifth major hurricane (Rita) did not occur until September 21, and in 2004, the fifth major hurricane (Karl) arrived on September 19. Wunderblogger Cotillion has put together a nice page showing all the seasons with five or more major hurricanes. The last time we had five major hurricanes earlier in the season was in 1961, when the fifth major hurricane (Esther) arrived on September 13. This morning we continue to have three simultaneous hurricanes, Hurricanes Igor, Julia, and Karl. This is a rare phenomena, having occurred only eight previous years since 1851. The last time we had three simultaneous hurricanes in the Atlantic was in 1998. That year also had four simultaneous hurricanes--Georges, Ivan, Jeanne and Karl--for a brief time on September 25. There has been just one other case of four simultaneous Atlantic hurricanes, on August 22, 1893. The year 2005 came within six hours of having three hurricanes at the same time, but the official data base constructed after the season was over indicates that the three hurricanes did not exist simultaneously.
Also remarkable this year is that are seeing major hurricanes in rare or unprecedented locations. Julia was the easternmost major hurricane on record, Karl is the most southerly major hurricane on record in the Gulf of Mexico, and Earl was the 4th strongest hurricane so far north. This unusual major hurricane activity is likely due, in part, to the record Atlantic sea surface temperatures this year.
Figure 2. Triple trouble, day two: From left to right, Hurricanes Karl, Igor, and Julia roil the Atlantic at 9:45 am EDT, September 17, 2010. Image credit: NASA/GSFC.
Hurricane Karl put on a burst of intensification this morning unprecedented in this part of the Atlantic, bottoming out as a Category 3 hurricane with a 957 mb pressure and winds of 120 mph. Karl's pressure dropped 10 mb between 1am EDT and 7 am EDT, but the pressure during the Hurricane Hunters' latest pass through the eye, at 10:12 am, had risen 12 mb, likely indicating that Karl's winds may weaken quickly in the next few hours. Karl is getting very close to land, and interaction with land will probably limit further intensification. Mexican radar out of Alvarado shows the eye is very close to the coast.
Figure 3. Radar image of Karl approaching landfall in Mexico. Image credit: Mexican Weather Service.
Impact of Karl on Mexico
Given that the Bay of Campeche coast has never experienced a hurricane as strong as Karl, its impact is likely to cause unprecedented damage to a 50-mile wide coastal area between Veracruz and Poza Rica. The strongest hurricanes in history to affect the region were Item in 1950, with 110 mph winds, Janet in 1955, with 100 mph winds, and Diana of 1990, with 100 mph winds. Flooding from Janet killed over 800 people in Mexico. and flooding from Diana killed at least 139 people. Fortunately, the Mexicans have one of the best disaster preparedness programs in the world, and it is likely that evacuations from the storm surge zone of Karl will greatly limit the loss of life from storm surge. The section of coast expected to receive Karl's maximum 12 - 16 foot storm surge is moderately populated, but is low-lying only in limited regions. Of greatest concern are Karl's torrential rains, since the region has high mountains near the coast that will experience extreme rainfall and flooding. Karl's high winds are also a major concern, and these winds are likely to damage thousands of buildings near the coast.
Hurricane Igor has slowly weakened over the past day, but remains a large and dangerous Category 3 hurricane with 120 mph winds. Igor passed just north of buoy 41044 last night, and the buoy recorded a lowest pressure of 942 mb. Top winds during Igor's passage were sustained at 74 mph, but this reading was on the weak left front side of the hurricane. The buoy recorded a significant wave height of 38 feet (the significant wave height is the average of the highest 1/3 of the waves.)
Figure 4. Morning satellite image of Igor.
Intensity forecast for Igor
Wind shear is low to moderate, 5 - 15 knots, and is expected to remain in this range through Saturday afternoon. Waters are warm, 29°C, and will remain 29°C through Saturday morning, then slowly decline. Igor is well armored against any intrusions of dry air for at least the next two days. These conditions should allow Igor to remain at major hurricane status through Saturday afternoon. It is possible the hurricane will undergo another eyewall replacement cycle, where the eyewall collapses and a new eyewall forms from an outer spiral band. This will weaken the hurricane by 10 - 20 mph if it occurs, but Igor may regain its lost intensity once the cycle is over, as it has done after its previous two eyewall replacement cycles. By Saturday afternoon, the trough of low pressure steering Igor northwestwards should bring moderate wind shear of 10 - 20 knots to the storm, potentially weakening it. The SHIPS models predicts shear will not rise to the high range, 20 - 30 knots, until the hurricane reaches the island, which may be soon enough to induce substantial weakening by perhaps 20 - 30 mph before Igor arrives at Bermuda. Igor will still probably be at least a Category 2 hurricane on its closest pass by Bermuda on Sunday night, and perhaps a Category 3. NHC is giving Bermuda a 29% chance of experiencing hurricane force winds from Igor, but this probability is likely too low. The Bermuda Weather Service is calling for Category 2 hurricane conditions for the island on Sunday, with 20 - 40 foot waves in the offshore waters, and 6 - 12 foot seas in the inland waters.
Igor's impact on Bermuda
The track forecast for Igor remains unchanged. Igor is moving northwest, in response to the steering influence of a broad trough of low pressure moving across the Western Atlantic. This trough will steer Igor to the northwest and north over the next three days, bringing the core of the storm very close to Bermuda late Sunday night. Igor is a huge storm, and tropical storm force winds extend out 290 miles to the north of its center. As the hurricane moves north, it will expand in size, as it takes advantage of the extra spin available at higher latitudes due to Earth's rotation. By Saturday night, Igor's tropical storm force winds are expected to extend outwards 320 miles from the center. Igor will be moving at about 11 - 13 mph during the final 24 hours of its approach to Bermuda, so the island can expect a period of 39+ mph tropical storm force winds to begin near midnight Saturday night--a full 24 hours before the core of Igor arrives. Igor will speed up to about 15 mph as it passes the island near midnight Sunday night, and Bermuda's battering by tropical storm force winds will not be as long as Igor moves away, perhaps 10 hours long. Hurricane force winds will probably extend out about 60 miles from the center when the core of Igor reaches Bermuda, and the island can expect to be pounded by hurricane force winds for up to 6 - 8 hours. In all, Bermuda is likely to suffer a remarkably long 36-hour period of tropical storm force winds, with the potential for many hours of hurricane force winds. Long duration poundings like this are very stressful for buildings, and there is the potential for significant damage on Bermuda. However, buildings in Bermuda are some of the best-constructed in the world, and damage on the island will be much lower than might otherwise be expected.
Bermuda's hurricane history
Igor is similar in strength and projected track to Hurricane Fabian of 2003. Fabian hit Bermuda as a Category 3 hurricane with 120 mph winds. It was the most damaging hurricane ever to hit the island, with $355 million in damage. Fabian's storm surge killed four people crossing a causeway on the island. These were the first hurricane deaths on Bermuda since 1926. The most powerful hurricane on record to strike Bermuda was the Category 4 Havana-Bermuda Hurricane, which hit on October 22, 1926, with 135 mph winds. The hurricane sank two British warships, claiming 88 lives, but no one was killed on the island. The deadliest hurricane to affect the island occurred on September 12, 1839, when a Category 3 hurricane with 125 mph winds and an 11-foot storm surge hit, tearing off the roofs of hundreds of buildings and wrecking several ships. An estimated 100 people were killed (source: Encyclopedia of Hurricanes, Typhoons, and Cyclones, by David Longshore.)
Igor's impact on the rest of the Atlantic
The models have been in substantial agreement over multiple runs that Igor will miss the U.S. and Canadian coasts--with the possible exception of southeast Newfoundland, which the ECMWF model predicts could see a close pass by Igor. The chief danger to the U.S. and Canada will come in the form of high waves. Large swells from Igor are pounding the Bahamas, Puerto Rico, and the Northern Lesser Antilles Islands, and will spread westwards to the U.S. East Coast today. By Saturday, much of the East Coast from northern Florida to Cape Cod Massachusetts can expect waves of 3 - 4 meters (10 - 13 feet), causing dangerous rip currents and significant beach erosion. These waves will continue through Sunday then gradually die down. The latest NOAA marine forecast for Cape Hatteras, North Carolina calls for 6 - 11 foot waves on Saturday night, and 9 - 13 foot waves on Sunday.
Strong upper level winds from big brother Igor are creating a high 20 - 30 knots of shear over Hurricane Julia this morning, and the hurricane is destined to weaken to a tropical storm soon. The high shear has eroded away the northwestern portion of Julia's heavy thunderstorms, and should be strong enough to destroy Julia by early next week. Julia is not expected to threaten any land areas.
Unusually quiet in the Pacific
The unusually quiet Western Pacific typhoon season has its 11th named storm of the season, Typhoon Fanapi. Fanapi, a Category 1 storm, is located 400 miles east of Taiwan, and is expected to intensify into a Category 2 storm before making landfall on the island Sunday. Ordinarily, the Western Pacific should be up to seventeen named storms by now. It has also been unusually quiet in the Eastern Pacific. On average, that ocean basin should have had 11 named storms, 6 hurricanes, and 2 intense hurricanes by now. This season, we've had about half the normal activity--just 6 named storms, 3 hurricanes, and 1 intense hurricane.
Elsewhere in the tropics
The ECMWF model develops a new tropical depression a few hundred miles off the coast of Africa 4 - 5 days from now. The GFS and NOGAPS models have backed off on their predictions of a Caribbean development late next week.
I'll have an update this afternoon.
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