From Category 2 prior to making landfall on Saipan in August, to being upgraded to Category 3 a month later, Typhoon Soudelor is now classified as a Category 4 tropical cyclone, based on assessments done by the National Weather Service in Guam and the University of Guam-Water and Environmental Research Institute.
Revising their earlier assessment in September, which said that Soudelor had peak over-water wind speed of 127 miles per hour or 110 knots with gusts of up to 150 mph or 130 knots, NWS and UOG made slight changes to the wind strength enough to raise Soudelor to Category 4.
“The team has now raised its estimate of Soudelor’s equivalent over-water intensity to the 130-mph (113-knot) sustained wind threshold of a Category 4 typhoon. The typical peak gust associated with a tropical cyclone of this intensity is 165 mph (143 knots),” NWS and WERI said.
The wind assessment was done by NWS Forecast Office Guam warning coordination meteorologist Charles Guard and WERI meteorologist Dr. Mark Lander.
The wind strength was raised after the team reanalyzed more than 100 original damage pictures obtained on-site and assessing some new damage information from subsequent visits.
They also analyzed other factors relating to typhoon intensity, such as the measurements of the minimum central pressure and the characteristics of Soudelor’s eye on satellite imagery.
The team already noted earlier that some of the damage on Saipan was consistent with even stronger gusts that were at-or-above the Category 4 threshold.
According to them, gusts of this magnitude are capable of causing the type of extensive damage seen in portions of central Saipan.
“The central west coast of the island had some of the most impressive wind damage, with healthy mature ironwood trees uprooted or snapped at the trunk. Patches and swaths of heavier wind damage are readily explained by turbulent wind flow across complex terrain,” their statement said.
However, not every part of the island experienced these peak winds. Based on their assessment, the north and south ends of the island were spared the worst because those locations were not located under the inner portion of the eyewall.
Despite upgrading its strength, NWS and WERI still doesn’t confirm the occurrence of tornadoes as some residents claimed.
“The presence of some trees in close proximity felled in opposite directions was thought by some to be evidence of tornadoes, but most, if not all, of the treefall pattern is consistent with the large-scale swirling cyclonic flow of the typhoon itself,” they said.
NWS and WERI said the large-scale swirling wind of the typhoon with a sustained wind and peak gust of a single magnitude of 130 mph and 165 mph would be an appropriate metric for all the observed effects of the typhoon.
“The patches of heavier damage are now viewed as areas where, for reasons of complex terrain and exposure, the peak over water gust of 165 mph was experienced in full force for an extended period of time,” they added.