The 2008 hurricane season: Ike follows close on the heels of Gustav and Hanna.
20 November 2020
01 September 2008
by Cecilie Wettre, Alexander Jacob and Jochen Kerkmann (EUMETSAT)
The hurricane season of 2008 was forecast to be an above average season, with 12 to 16 storms, six to nine hurricanes, and two to five major hurricanes predicted. With hurricanes/tropical storms Gustav, Hanna, Ike and Josephine in rapid succession across the Atlantic, the forecasts of an active season were indeed verified.
Ensuring the safety of human lives is one of the main priorities in severe weather situations like these and in order to be able to do so storms and hurricanes like Gustav, Hanna and Ike are loosely monitored by geostationary satellites operated by EUMETSAT and the National Oceanic and Atmospheric Administration (NOAA). The Advanced Scatterometer (ASCAT) instrument aboard EUMETSAT's Metop polar-orbiting satellite is also contributing important measurements of wind speed and direction. These measurements are currently being evaluated by the Dutch Weather Service on behalf of EUMETSAT under the umbrella of the Ocean & Sea Ice SAF.
Metop-A ASCAT products showing Hurricane Gustav
The storms are also monitored by the new Jason-2 ocean altimetry satellite. The top images below show, on the left, the wind speed of hurricane Gustav as measured by Jason-2 on 26 August, while the image to the right shows the satellite (altimetry) derived Sea Level Anomaly calculated the same day (the coloured dots mark the trajectory of Gustav).
Sea surface height anomalies are strongly related to the internal thermal structure of the ocean. A higher sea surface than normal corresponds to a deep layer of very warm water. The heat energy contained in such a deep layer of the ocean can fuel hurricanes as they pass over. This is why altimeter data from satellites such as Jason-2 are important in order to forecast the strength of individual hurricanes and even to predict the number and strength of hurricanes expected in a given season.
After ravaging the Caribbean and the United States, ex-Hurricane Ike moved to Canada and then back across the Atlantic as an extratropical cyclone, as observed by EUMETSAT's Meteosat-9 satellite (see Airmass RGB Image (17 Sep 12:00 UTC) and case study Hurricane Alex makes the transition to an extra-tropical cyclone, 5 August 2004) .
Low pressure delivered strong winds when the air masses received added momentum down the mountain slopes of Greenland, where some settlements reported gales from the north-west. The interaction between swells and wind waves from Ike produced nine-metre-high waves in the Denmark Strait between Greenland and Iceland. South-eastern Greenland also experienced the remnants of Ike with gale force winds and local 'Piteraq', an autumn wind blowing down from the ice shield.
The Iceland Meteorological Office reported that Hurricane Ike contributed moisture and momentum to a low pressure system just west of Iceland on Tuesday evening and into Wednesday morning, 16–17 September, with unusually high, albeit not record-breaking, amounts of precipitation. Some 200 millimetres of precipitation were measured close to Reykjavik in 24 hours, reaching as much as 18–20 millimetres an hour at its most intense. Gusts of up to 40 metres per second were measured.
This is not so unusual for this time of year; the difference is that the weather was bad everywhere on Iceland. Normally it would be relatively quiet in the north-east, when storms are raging in the south-west, and vice versa. Remains of former tropical hurricanes reach Iceland only every second to fourth year.
After Iceland, Ike finally died away, almost three weeks after the low pressure system was formed near Cape Verde off the west coast of Africa. It happens only once or twice a year that the remains of a hurricane manage to travel all the way to the northern latitudes. Normally the weather systems will fizzle out while passing the high pressure belt around 30 degrees north of the Equator.
QuikScat scatterometer winds, 31 Aug, 11:22 UTC (Credit: KNMI)
Terra MODIS True-colour RGB Image, 30 Aug, 16:05 UTC (Credit: NASA)
Terra MODIS True-colour RGB Image, 31 Aug, 16:45 UTC (Credit: NASA)
Metop-A AVHRR day microphysics RGB Image, 31 Aug, 15:10 UTC
Metop-A AVHRR day microphysics RGB Image, 1 Sep, 14:49 UTC
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