Australia cleans up from Larry

Emergency work continues in the Queensland territory of Australia, where Tropical Cyclone Larry roared ashore Sunday near the town of Innisfail as a major Category 3 hurricane with sustained winds of 118 mph and gusts to 180 mph. Larry caused tremendous damage to crops and buildings, causing at least $400 million in damage and leaving 7000 people homeless. Fortunately, no deaths or major injuries occurred. Larry may be the strongest tropical cyclone to affect the east coast of Australia, and the most damaging cyclone to affect Australia since Tropical Cyclone Tracy devastated Darwin on Christmas Eve in 1974, killing 71 and leaving 20,000 homeless.

Media reports continue to confuse people by referring to Larry as a Category 5 storm, and not clarifying that this was on the Australian severity category system, a one to five ranking system based on the maximum wind gusts of a storm. A storm that has wind gusts in excess of 174 mph (280 km/h) is classifed as a Category 5. In the U.S. Saffir-Simpson scale that we are familiar with, the strength of a storm is based on the sustained winds, not the gusts. According the Australian Bureau of Meteorology, Tropical Cyclone Larry at landfall had 118 mph sustained winds. Adam Moyer, a grad student at Penn State, just pointed out to me that the Australians use a 10-minute average to report their sustained winds, while the U.S. NHC uses a 1-minute average. Thus, the sustained 1-minute average wind speeds of Larry were probably closer to 130 mph--the high end of the Category 3 range on the Saffir-Simpson scale. Category 3 sustained wind speeds range from 111 to 130 mph. However, the maximum 1-minute sustained winds as estimated by the Joint Typhoon Warning Center were 115 mph, gusting to 145 mph. The Australians and the Joint Typhoon Warning Center both maintain their own "official" data bases of tropical cyclones, so we can see that for Larry these will disagree. This disagreement highlights some of the problems researchers who are attempting to make a connection between global warming and hurricane intensity have--which "official" data base do you use for the Southern Hemisphere? You get a different answer depending upon which database you use.


Figure 1. Tropical Cyclone Wati off the coast of Australia as a minimal hurricane with 75 mph winds.

What's up next for Australia?
Currently, Tropical Cyclone Wati (a Category 1 hurricane on the Saffir-Simpson scale), is just off the east coast of Australia in a location similar to where Larry came ashore. Wati is expected to recurve to the south and weaken over the next three days, but may come close enough to the coast for warnings and watches to be issued. On Australia's west coast, there is Tropical Storm Floyd to worry about. Floyd is expected to become a Category 2 hurricane by Thursday.

The Southern Hemisphere tropical cyclone season runs November through April, and there should be only one or two more tropical cyclones this Spring in the Southwest Pacific (off of the east coast of Australia) and the southern Indian Ocean (off of the west coast of Australia). So far, the hurricane season in the Southwest Pacific has been about average, and the hurricane season in the South Indian ocean has been below average.

For the Southwest Pacific so far this hurricane season, here are the storm numbers, followed by averages in parentheses:

Tropical storms: 7 (9)
Hurricanes: 4 (5)
Major hurricanes, Cat 3-4-5: 1 (2)

And for the South Indian ocean:

Tropical storms: 12 (17)
Hurricanes: 4 (9)
Major hurricanes, Cat 3-4-5: 3 (5)

Jeff Masters