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Matthew not strengthening; Igor is Newfoundland's worst hurricane in memory

By: Dr. Jeff Masters, 1:53 PM GMT on September 24, 2010

Tropical Storm Matthew is bearing down on the Nicaragua/Honduras coast, but wind shear is keeping the storm from intensifying this morning. A hurricane hunter aircraft is in Matthew, and found the center pressure had risen slightly, to 1002 mb, at 8:24am EDT. Top winds seen at the surface remained at 50 mph, but winds at their flight level of 5,000 feet peaked at an unimpressive 48 mph. Satellite loops show that Matthew's heavy thunderstorm activity is mostly on the storm's south side, and this is due to strong upper level winds out of the northeast creating a moderate 10 - 20 knots of wind shear over the storm. Heavy rain squalls have moved ashore over northeastern Nicaragua and Honduras, as seen in the latest observations from Puerto Lempira, Honduras.

Figure 1. The forecast radius of tropical storm force winds of 39+ mph (dark green colors) and 58+ mph winds (lighter yellow-green colors) taken from the official 5am EDT forecast for Tropical Storm Matthew. The image was generated from our wundermap for Tropical Storm Matthew with the "hurricane" layer turned on with "wind radius" and "forecast" boxes checked.

Short range forecast for Matthew
An upper-level high pressure system lies to the northwest of Matthew, near the coast of Belize. The clockwise flow of air around this high will bring a moderate 10 - 20 knots of wind shear over Matthew today and Saturday morning. There is some dry air to the north of Matthew, and the shear may be able to drive some of this dry air into the storm, slowing intensification and keeping Matthew below hurricane strength before it makes landfall in northeastern Nicaragua late tonight. Matthew's passage over the northeast corner of Nicaragua and northeast Honduras should also act to disrupt the storm. The terrain is not mountainous in this region, though, and Matthew should be able to reorganize quickly once it emerges back into the Western Caribbean on Saturday morning. By Saturday afternoon, Matthew will move more underneath the upper-level high, resulting in much lower shear. The SHIPS model forecasts that shear will fall to the low range, 5 - 10 knots, Saturday afternoon through Monday. This drop in shear may allow for intensification of Matthew into a Category 1 hurricane before it hits Belize on Sunday morning. However, a strong tropical storm is more likely.

Impact of Matthew on Nicaragua, Honduras, and Belize
Tropical storm force winds from Matthew are forecast to extend outwards from the center between 40 - 80 nm (46 - 92 miles) as the storm moves along the north coast of Honduras this weekend. Matthew's initial forward speed of 15 mph will slow to 10 mph by Sunday morning. In combination, these factors should bring tropical storm force winds of 39+ mph to Guanaja, Roatan, and the central Honduras coast beginning between 4am - 8am EDT Saturday. These winds will last about 6 - 12 hours. Given the current weak state of Matthew, I doubt winds in excess of 50 mph will be seen on the Honduras coast as the storm passes to the north. The coast of Belize will be subject to a longer period of strong winds, since Matthew will be moving slower when it hits Belize, and may be a stronger storm. Expect 39+ mph winds to arrive at the coast of Belize between 6 - 10 pm EDT Saturday night, and persist for 12 - 16 hours, near where the center of Matthew makes landfall. A good way to compute these times of arrival and duration is to use our wundermap with the hurricane wind radius forecast layer turned on (Figure 1.) The main danger for Honduras, Belize, Mexico, and northern Guatemala will be from heavy rains, not wind. The forecast rain amounts of 6 - 10 inches, with isolated amounts of 15 inches, will cause severe flooding and dangerous mudslides. Belize is probably most at risk from Matthew's rains.

Long range forecast for Matthew
Matthew is being forced just north of due west by a strong ridge of high pressure. This ridge will keep the storm moving at 15 mph through Saturday. On Sunday, a trough of low pressure diving southwards over the Eastern U.S. will weaken the steering currents over the Western Caribbean and cause Matthew to slow to just 5 mph by Sunday night. The models are divided into two basic camps on what might happen next. One solution, championed by the ECMWF, NOGAPS, and UKMET models, has Matthew continuing inland once it makes landfall in Belize Sunday morning or afternoon. This solution means Matthew would likely dissipate over Mexico's Yucatan Peninsula. The other solution, given by the GFS, GFDL, and HWRF models, predicts Matthew will move inland over Belize for a day or so, then drift northeast and pop back out into the Western Caribbean sometime Monday or Tuesday. The key to Matthew's long range track depends upon how it interacts with a tropical low pressure area developing in the Eastern Pacific, and the trough of low pressure over the Eastern U.S. With steering currents expected to be weak, and small changes in Matthew's track making the difference between the storm being over land or water, the long range forecast for the storm is highly uncertain. It Matthew lingers in the Western Caribbean off the coast of the Yucatan Peninsula for several days, the potential exists for the storm to grow into a large and dangerous major hurricane. Sea surface temperatures and the total heat content of the Caribbean in this region are greater than the previous record highs set in 2005 (Figure 2), so there is plenty of fuel for a hurricane.

Figure 2. Total oceanic heat content (called the Tropical Cyclone Heat Potential, or TCHP) in kilojoules per square centimeter (kJ/cm^2), for September 22 2010 (top) and the previous record high for this time of year, set in 2005 (bottom.) Category 5 Hurricane Wilma of 2005, the strongest hurricane on record in the Atlantic, reached its peak strength over the "bullseye" of high TCHP over the Western Caribbean. TCHP values are even higher this year than when Wilma formed, and TCHP in excess of 90 kJ/cm^2 (orange colors) is commonly associated with rapid intensification of hurricanes. Image credit: NOAA/AOML.

Tropical Storm Lisa
Tropical Storm Lisa continues to churn the waters of the far Eastern Atlantic. By Saturday night, upper level winds out of the west are expected to increase, bringing high wind shear of 20 - 45 knots over Lisa. The high shear may be capable of destroying the storm by early next week. It appears unlikely that Lisa will affect any land areas.

Elsewhere in the tropics
There are no other threat areas to discuss, and the GFS and NOGAPS models have backed off on their predictions of a new tropical depression forming in the Caribbean 6 - 7 days from now.

Hurricane Igor: Newfoundland's worst hurricane in memory
Newfoundland, Canada continues to reel from the effects of the punishing blow delivered by Hurricane Igor on Tuesday. The island remains devastated with many communities isolated by washed out bridges and roads. Power is impossible to restore in many areas since service crews cannot get there. The entire eastern portion of Newfoundland was cut off from the rest of the province due to a massive ravine that carved its way through the Trans-Canada Highway (Figure 3.) The road was re-opened yesterday using a temporary bridge. A summary of the impact of Igor prepared by Environment Canada puts it this way:

"Hurricane Igor and its severe impacts certainly represent a rare event in Newfoundland history which has been described as the worst in memory. In statistical terms, this was effectively a 50 - 100 year event depending on how one chooses to define it. There are no hurricanes/post tropical events of this magnitude striking Newfoundland in the modern era. Hurricane Juan in Nova Scotia was the last Atlantic Canadian hurricane to cause extreme damage. Prior to the naming of hurricanes, the 1935 Newfoundland Hurricane 75 years ago was of similar intensity."

Figure 3. A ravine carved by Hurricane Igor's flood waters washed out the Trans-Canada Highway, isolating Southeast Newfoundland from the rest of the province. Image credit: CBC News.

Igor made it all the way to southeast Newfoundland as a Category 1 hurricane, and brought sustained winds above hurricane force of 76 mph to two stations, Cape Pine and Bonavista. The storm's peak wind gust was 107 mph at Cape Pine. Igor brought sustained winds of 58 mph, gusting to 85 mph, to Newfoundland's capital, St John's. The city recorded a remarkably low pressure of 958 mb, and picked up 3.99" of rain during Igor's passage. Nearby St. Lawrence recorded its greatest 1-day rainfall event in its history, 238 mm (9.37".) Many other stations recorded 150+ mm of rain, making Igor a 1-in-100 year rainfall event. Igor's record rains were due, in part, to the storm's large size, and to the record warm sea surface temperatures over the Atlantic that allowed large amounts of water vapor to evaporate into the air surrounding Igor. Widespread rain amounts of 5 - 9 inches fell over much of southeast Newfoundland's rocky terrain, which is unable to absorb so much water. The resulting severe flooding washed out hundreds of roads, collapsed several major bridges, and forced numerous rescues of people trapped on the second stories of their homes by flood waters. Igor generated swells of 6 - 8 meters (20 - 26 feet) that pounded the southern coast of Newfoundland; significant wave heights reached 39 feet at the Newfoundland Grand Banks Buoy, and a storm surge of a meters (3.28 feet) hit the northeast shores of Newfoundland. Igor killed one person on Newfoundland, and damage may exceed $100 million, making Igor the most damaging tropical cyclone in its history.

While it is unusual for full-fledged hurricanes to affect Newfoundland, It is not that unusual for hurricanes to penetrate as far north as Newfoundland's latitude; over 40 hurricanes have done so. The last time this occurred was in 2003, when Hurricane Fabian made it to latitude 48.7°N as a hurricane. The all-time record is held by Hurricane Faith of 1966, which followed the Gulf Stream and maintained hurricane status all the way north to latitude 61.1°N, just off the coast of Norway.

Figure 4. Igor caused drastic beach erosion at Elbow Beach in Bermuda. Image credit: Extreme weather photographer Mike Theiss. He has a nice web page documenting his experience with the storm on Bermuda.

Next post
If there's a significant change to Matthew or to the forecast, I'll have an update this afternoon. Otherwise, I'll post an update Saturday by noon.

Jeff Masters


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