I just wanted to put out a brief update on Hurricane Iselle, which is still a category 1 hurricane and is heading for Hawaii. It’s not unheard of for Hawaii to be impacted by tropical cyclones, however, it is very rare. Hurricane Iselle currently has sustained winds of 90 mph with gusts up to 115 and is moving west northwest at 16 mph. It is expected to make landfall sometime Thursday evening. A few hours ago, Iselle began to re-strengthen with convection wrapping symmetrically around its eye, however, some weakening seems to have occurred over the last couple of hours.
Hurricane Iselle has taken on the characteristics of what is known as an annular tropical cyclone. These types of tropical systems feature a large, symmetric eye with intense convection wrapping around the eye. These rare types of tropical systems are not influenced as much by poor environmental conditions and often weaken much slower than typical hurricanes. That’s why forecasting the intensity of these types of systems can be tricky. However, it does look like Iselle has lost the typical structure of an annular tropical cyclone over the last couple of hours, which means it could be weakening.
Hurricane Iselle is currently moving over some cooler waters, but wind shear overall has been weak, which is likely what has allowed Iselle to strengthen some today. Iselle will move over slightly warmer waters as it moves closer to Hawaii; however, wind shear will most likely increase as it makes its way further west.
Hurricane warnings have been issued for the Big Island, so expect hurricane force winds in that region. Heavy rains and flooding will also be a big threat with this system. Historically, Hawaii has never been hit by a hurricane coming from the east, so if Iselle were to maintain its hurricane status upon landfall, this would make history. Since 1949, the Hawaiian Islands have only been directly hit by a hurricane twice, one in 1959 and 1992.
I’ll continue to keep a close watch on everything tonight. Please continue to follow Firsthand Weather on Facebook, where plenty of updates will be put out on Iselle throughout tonight and tomorrow.
Matthew Holliday is a graduate of the University of Oklahoma, where he completed a B.S. in Meteorology and a B.S. in Geographic Information Science. He is currently pursing his master's degree in meteorology and climatology at Mississippi State University. Matthew founded Firsthand Weather in 2010 as a senior in high school and maintained the site through his undergraduate career. Research that was conducted by Matthew while at OU involved determining the synoptic environment in which various types of wave clouds (including vertically propagating waves and trapped waves) develop in Boulder, Colorado and Norman, OK. Matthew also did research on spatial changes in tornado activity across the United States . The goal of this study was to determine if spatial changes in tornado activity had occurred and if those changes could be linked to changes in average surface dew point temperature. Matthew has completed coursework in dynamics, thermodynamics, cloud physics, calculus and differential equations, statistics, remote sensing, GIS, synoptic meteorology, and mesoscale meteorology. His goal is to provide his audience with a deeper understanding of what drives our weather and climate, while making it easy and enjoyable to learn.