Hurricane Matthew strengthens rapidly

Another unprecedented event is taking place in this year of unusual tropical cyclones. Hurricane Matthew is heading for Jamaica, from the south.

It has already taken an unusual track; coming from Martinique as a Tropical Storm, Matthew headed west-southwestwards towards Colombia, strengthening to category 3 as defined by the Saffir-Simpson Scale.

On Friday night the hurricane was within 120km of Punta Gallinas, the most northerly point of South America. This is as close as any hurricane has been recorded as coming to the continent.

It had, in the previous 12 hours, strengthened to become a category 5 hurricane. USAF aircraft had recorded winds of 265 kilometres an hour within the eye wall, the place of strongest winds.

Overland, this intensity would cause catastrophic damage but for the following 24 hours, at least, the threat is over Caribbean waters.

Hurricane Matthew is unusual too because it is the lowest latitude Category 5 hurricane to have been known, and one of only six cat 5s to have been recorded with such intensity after September.

Worryingly, the water temperatures are above average in the Caribbean, and not just on the surface but to some depth. This makes it more likely that Matthew will maintain at least Category 4 strength for the next two days.

When hurricanes pass over the water, they tend to churn up colder water from below so cutting off their own energy supply and limiting development. In the case of Hurricane Matthew, the churning brings up more warm water, more energy for the hurricane.

This is a positive feedback loop and is horribly reminiscent of the conditions that allowed Typhoon Haiyan to destroy the Philippine city of Tacloban in 2013. Haiyan was the deadliest Tropical Cyclone on record and the most intense at the point of landfall.

Hurricane Matthew is very likely to churn through Jamaica on Monday as at least a Category 4 cyclone. Only two hurricanes even of Category 4 strength have affected Jamaica, both in this century.

Ivan, in 2004, passed to south but brought hurricane force winds, killed 17 people and left $360m worth of damage. In 2007, Hurricane Dean also passed to the south, causing extensive damage and killing three people.

In fact, Jamaica doesn’t often receive direct hurricane hits. Florida State University found that Jamaica experienced landfalls of the eye of a hurricane only 12 times between 1886 and 1995. None of these was a Category 5.

Of all hurricanes that have hit Jamaica since 1851, the start of reliable records, none has approached from the south, except one. In 2012, Hurricane Sandy came up from the south as a Category 2 hurricane.

Hurricane Matthew is likely to be at least a Category 4 at landfall on Jamaica. It is then likely to hit eastern Cuba and affect western Haiti. In addition to the hurricane force winds and battering waves, rain will be torrential.

Forecasts suggest a typical 250mm of rainfall, up to 600mm in places and given the geography, flash floods and landslides are inevitable.

Immediately after Jamaica, eastern Cuba is likely to receive direct hit. Some of the strength of Matthew will have been lost to the Jamaican mountains but it is still forecast to be a Category 4 hurricane on arrival.