(Tropical Storm Alberto in 1988 formed slightly further north at 41.5degN). Grace is also unusual in that the storm formed over sea surface temperatures of only c23degC. Normally, tropical storms require temperatures in the region of 26-27degC to form and be self sustaining.

Grace looks as though she will bow out today, and transition into an extra tropical storm.

Reaching the end of the Atlantic Hurricane season we can stop and reflect at what has been an eventful and record breaking year; five major hurricanes, eight tropical storms and a total of 16 named storms. Pre-season forecasts in December 2007 suggested that we should expect an ‘above average’ season (ie relative to the 1950-2005 baseline) and the consensus view as the season developed was for this situation to become well above average through 2008.

Image courtesy of Jeff Master's Wunder Blog at wunderground.com/blog/JeffMasters

The Season in review
The season began at the end of May two days earlier than the official start date with Tropical Storm Arthur making landfall on Belize.

Arthur was the first tropical storm to form in May since Tropical Storm Arlene in 1981. Arthur was an interesting transitional storm—having formed from the remnants of tropical storm Alma. Arthur was also unusual in that the first advisory position for the storm was inland over northern Belize, about 30 miles from the ocean.

The storm’s maximum sustained winds were near 40 mph (65 km/hr), with higher gusts, mainly over water east of its center. Hurricane Arthur rapidly intensified when it hit Belize causing torrential rain and flash floods. The storm claimed five lives and damages were estimated at $78million.

The rest of June was quiet, but was followed by the first major hurricane of the season – Hurricane Bertha (Category 3). Hurricane Bertha became the longest-lived named storm on record in July in the Atlantic Basin (17 days).

Bertha also formed farther east than any other on record so early in the season (east of 250W as a storm and 500W as a hurricane). It began its journey on 3rd July over the Atlantic Ocean and peaked at 120mph sustained winds on 7th July.

It did not make landfall and weakened as it approached Bermuda but produced rain and tropical storm winds. No losses were reported.

August proved to be an active month with Tropical Storms Eduoard and Fay, and Hurricanes Gustav and Hanna. All four made landfall with Tropical Storm Fay bringing heavy rain and wind to the island of Hispaniola. Tropical storm Fay stuck Florida a record four concurrent times claiming 36 lives and an estimated $180million damage.

Of these four windstorms, August produced the second most devasting and significant hurricane to the insurance industry of the season with Gustav. At its peak it was a Category 4 storm before making landfall in Cuba. It made landfall at the Island of Hispaniola and Jamaica but at this point it was still only a tropical storm.

It was then upgraded to hurricane status on 29th August where it caused most of its damage having been labelled as Cuba’s worst hurricane in 50 years. After Cuba, Gustav then moved across the Gulf of Mexico towards the US where the biggest evacuation in US history of 2 million people took place in Southern Louisiana including many from New Orleans as fear of a potential repeat of Hurricane Katrina in 2005 loomed. 

Estimates of economic damage from Gustav were placed at $18billlion and 138 deaths. Insured industry losses are estimated at $4 billion (Sigma).

Ike will be remembered for being a strong Category 2 storm at landfall in the US; however, it wrought much damage in the Caribbean as a Category 4 hurricane.

Ike’s impact was sufficiently significant. $6.3million was called upon by the CCRIF to help satisfy the short term financial needs of Grand Turk, where 85% of buildings were damaged or demolished (Source: CCRIF).

Ike weakened significantly as it passed over Cuba, but gained strength as it moved westward across the Gulf of Mexico.

There were some interesting similarities with Katrina. Ike passed over a warm pool eddy that helped to strengthen the storm, and underwent an eye-wall replacement before landfall on Galveston Island on 13 September.

At landfall Ike was a strong Cat 2 storm (with wind speeds just shy of the next category on the Saffir-Simpson scale), but had pressure and wind field dynamics analogous to a Cat 3 or 4 storm.

The physical extent of the storm was greater than that of Katrina. This is evident by comparing the statistics of Ike at the time and Katrina as Ike travelled over the Gulf of Mexico. Ike had a tropical storm force winds radius of 275 miles compared to Katrina’s 230 miles, and hurricane force winds radius of 115 miles compared to Katrina’s 105 miles.

Ike impacted downtown Houston and Galveston in Texas when it made landfall. Galveston suffered much of its damage through flooding resulting in an outage of power.

PCS released an initial insured US property loss estimates for Hurricane Ike at $8.1 billion (30 Sept) which was subsequently readjusted to $10.7 billion (5 Dec) not including offshore.

The overall damage caused by Ike included power outage, storm surge, wind damage and property damage to Ohio, Texas, Kentucky, Indiana and Illinois amongst others (Source: PCS).

Ike was particularly devastating due to the unusual introduction of an extra tropical front as it made landfall resulting in Ohio facing high force winds.

Records broken by Ike: The diameter of the tropical storm was 275 miles. This makes it the largest Atlantic hurricane recorded. It also had the second highest integrated kinetic energy at 5.2 (IKE = scale 1-6) of any Atlantic storm (Source: Weather Underground).

Just as we expected Hurricane season to be reaching its nadir, Hurricane Paloma (Category 4) closed in across the Cayman Islands and Cuba in November forcing 1.2 million people to be evacuated (Source: USA Today). The storm ended on the 9th November to draw a close to Hurricane Season 2008. Hurricane Paloma is only the 4th “P-named” hurricane since records began.

The 2008 season closed within the traditional end of November timeframe.

Records set  in 2008
• Fourth costliest hurricane season on record ($21billion dollars in U.S. damage, according to ISO’s Property Claim Services)
• First time major hurricanes have been observed in five separate months (Bertha, Gustav, Ike, Omar, Paloma occurred in July, August, September, October, and November, respectively)
• First time six consecutive storms made U.S. landfall (Dolly, Edouard, Fay, Gustav, Hanna, and Ike)
• First time three major hurricanes have hit Cuba (Gustav, Ike, Paloma)
• Costliest hurricane in Texas history (Ike, estimated onshore industry loss $15bn)
• Second deadliest US hurricane since 1972, and 26th deadliest in history (Ike, with 82 dead)
• Highest wind gust ever measured in a hurricane over land (Gustav, 212 mph in Pinar del Rio, Cuba)
• First storm ever to make four landfalls in one state (Fay, in Florida)
• Second strongest November hurricane (Paloma, 145 mph winds)
• Smallest tropical cyclone on record (Marco)
• Longest-lived July hurricane on record, longest-lived hurricane so early in the season, longest-lived tropical storm in July and so early in the season (Bertha, which was a hurricane 7.75 days, eclipsing the previous record of 7 days held by Hurricane Emily of 2005. Bertha was at tropical storm strength or greater for 17.25 days)
• Farthest east forming tropical storm and hurricane for so early in the season (Bertha)
• Hurricane Ike had the highest integrated kinetic energy in history

Hurricane season Average 1944-2002 vs 2008

Links

• 30 Deadliest US Hurricanes
• 30 Costliest US Hurricanes
• 30 Deadliest Atlantic Hurricanes
• Top 10 Most Active Hurricane Seasons

Sources

• BBC Weather 
• The Weather Channel
• Hurricane Central
• Earth observatory, Nasa
• Jeff Master’s Wunderblog
• Klotzbach and Gray, Tropical Meteorology Project
• TSR