UK Met Office predicts 20 tropical storms

The United Kingdom’s National
Weather Service on Thursday predicted 20 tropical storms in the Atlantic Ocean
between July and November.

In addition, the Met Office
predicted the Accumulated Cyclone Energy index – a measure of the storm
lifetimes and intensities as well as total numbers over a season – was likely
to be 204, well above the 1990–2005 average of 131.

“This would make it one of the most
active tropical storm seasons on record,” the UK Met Office said on its
website. “In the last 40 years, only 2005 has seen more storms in the July to
November period with 25 recorded, and only three seasons (1995, 2004 and 2005)
have recorded a higher ACE index than 204.”

The Met Office forecast, which
comes out a little later than many of the other well-known hurricane forecasts,
has given good indication of Atlantic tropical cyclone activity in the past. It
was able to identify the relatively quiet seasons of 2007 and 2009 from the
active season of 2008.

Of local note, in September 2004
the Met Office had the only major computer model to accurately forecast several
days out the track of Hurricane Ivan close to Grand Cayman. All the other
models showed the storm curving north before it reached Grand Cayman.

Matt Huddleston, principal
consultant on climate change at the Met Office spoke about the usefulness of
hurricane season predictions.

“North Atlantic tropical storms
affect us all through fluctuating oil, food and insurance markets,” he said.
“The Met Office forecast has demonstrated its benefits over recent years
through the accuracy of its predictions.”

This year the Met Office has moved
to a new prediction system called GloSea4, which it believes will further improve
the accuracy of the forecast.

The forecast also uses information
from the seasonal prediction system of the European Centre for Medium Range
Weather Forecasts, something noted Colorado State University scientist Phil
Klotzbach has praised in March as very good a predicting the El Niño Southern
Oscillation.

The Met Office stated that one of
the key indicators for a tropical storm season is the situation El Niño, an
anomaly that affects sea surface temperatures in the tropical Pacific and wind
shear levels in the Atlantic.  The
wind-shear causing El Niño that existed during the calm 2009 hurricane season
has collapsed and there are now neutral conditions. However, the ECMRWF is
predicting a La Niña to form by July or August, something that would reduce
wind shear in the Atlantic for the peak part of the hurricane season.

The UK Met Office forecast follows
other forecasts – which also take into account the month of June – calling for
a very active hurricane season. On 4 June, Tropical Storm Risk predicted 17.7
named storms, 9.5 hurricanes and an Accumulated Cyclone Energy index of 182. On
2 June, Klotzbach and his Colorado State associate William Gray predicted 15 to
18 named storms, 8 to 10 hurricanes and an Accumulated Cyclone Energy index of
185. On 27 May, the US Climate Prediction Centre, in cooperation with the
National Oceanic and Atmospheric Administration and the National Hurricane
Centre predicted 14 to 23 named storms, 8 to 14 hurricanes and a 70 per cent
chance the Accumulated Cyclone Energy index would fall between 155 and 270.

Several tropical weather
forecasters have noted that the record-high sea surface temperatures, reduced
trade winds and lower atmospheric pressures in the tropical Atlantic are ominous
signs for the hurricane season.  In
addition, meteorologist Jeff Masters wrote in his Weather Underground blog on
Wednesday that the formation of a named storm in the tropical Atlantic south of
22°N and east of 77°W in June or July could be a harbinger of an active hurricane
season.  Invest 92L, which formed last
week, came very close to being classified a tropical cyclone, but eventually
disintegrated because of wind shear.

“The formation of a storm in this
region during June or July is one factor the NOAA and Colorado State University
seasonal hurricane forecast teams have used in the past as a predictor for an
active season in their early August forecasts,” Masters wrote. “Now, 92L didn’t
make it to named storm status, though it was pretty close to being a tropical
depression. However, the near-formation of 92L into a tropical depression is,
in my mind, a clear harbinger that we can expect a severe hurricane season this
year. It’s very rare to have a development like 92L in that portion of the
tropical Atlantic this early in the season. The lower than average wind shear
and higher than average [sea surface temperatures] that helped 92L get
organized are more likely than not to carry over into the main portion of
hurricane season, giving us a much more active hurricane season than normal.”