Hurricane Lane Thursday 23 August Impact Forecast for Hawaii

Not too much changed in the outlook overnight.  While Lane remains a Category 4 hurricane (125 kt/145mph winds), it should begin to more rapidly weaken as it passes just south of the Islands.  Here is the predicted wind swath map based on this mornings CPHC forecast:

On this track, aside from higher elevations and ridgelines, sustained winds should stay at or just below tropical storm force.  Lane will take about three days to pass the islands – that’s a long time for it to dump rain, and due to an effect called orographic amplification, there is a big risk of flooding and landslides.  Orographic amplification is caused by  warm moist air being forced upwards by higher terrain (“orography”), causing it to cool and drop out excess moisture.  In the case of tropical systems, it can take an already wet storm and double the rain rates or more on the upwind side (the downwind side is dried out to a corresponding degree).  Here’s a radar composite using the two stations on Hawai’i (at South Point/Naalehu and Upolu Point/North Kohala ) showing the first rain bands passing over the Big Island … due to the mountains, there are “gaps” in the coverage

Damage is *very* dependent on the exact track and rain totals.  Wobbles one way or the other matter a lot in this case, and exact timing of the sharp west turn can cause the damage to change by a factor of ten for only a 20 or 30 mile further north track shift, since it causes impacts on the densely developed south coast of Oahu to come in to play!  If you include economic impacts, the impacts are already in the 10’s of millions of dollars due to preparations, tourism, etc.  The long term impacts (once things settle out, some impacts will be recovered) will likely be in that range, but if the storm shifts even a little further north, or something breaks that shouldn’t, impacts in the 100’s of millions are very possible.

While we’re obsessing over Hawai’i, we shouldn’t forget that Japan – where flooding has killed hundreds this year – is being dumped on by another Typhoon, and and South Korea is being hit today as well.


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