Why Hurricane Forecasts Are So Difficult: West Coast Edition

norbert visible

uspacifi.cfThere’s a Category 3 Hurricane spinning in the Pacific off the coast of Baja California this afternoon. Later tonight Hurricane Norbert will hit a brick wall in the form of colder sea surface temperatures and quickly start losing strength.

In the short term this storm has caused no major forecast problems. In the longer range things get muddy.

A few days ago the GFS was bringing Norbert up the SoCal coast, making landfall near the OC/San Diego county line. Since then, Norbert’s guidance has been repositioned farther south with each model run. The GFS now brings Norbert on shore in Northern Baja California, just south of the Mexican border.

aep14_2014090612_track_lateThe well respected European model had taken Hurricane Norbert out to sea, never making land. It doesn’t swing quite as far west now, but the Euro still shows no landfall.

There is some agreement between the specialized tropical weather models. The spaghetti plot on the left shows agreement in a turn to the right, then a much weaker Norbert comes onshore in northern Baja.

It still looks like rain will be the major impact from Norbert. Here’s part of the latest Hurricane Center discussion.

There is high confidence in the short-term track forecast since there is a good guidance agreement. Beyond 3 days, global models either forecast Norbert to dissipate in situ near the west coast of the northern Baja California peninsula or continue to move the system eastward as a weak low or a trough. The NHC prefers the former global model solution.

Moisture from the remnants of Dolly and the Pacific ITCZ is being advected northward by the outer circulation of Norbert across northern Mexico and into the southwestern United States. This could result in heavy rains and life-threatening flash flooding in these areas during the next few days.

174208W5_NL_smNorthern Baja, the Mexican state of Sonora and extreme southern California and Arizona seem most susceptible.

There are a few factors which have made Norbert tough to forecast. The largest is the near total lack of steering winds over the next few days. The slower a hurricane’s forward motion, the less accurate the forecast is!

There is no doubt Norbert will rapidly lost its mojo as it enters cooler water. That’s the good news.

The bad news is Norbert’s moisture will still get dumped. Tropical weather systems have plenty of ways to get you beyond wind.

2 thoughts on “Why Hurricane Forecasts Are So Difficult: West Coast Edition”

  1. This could get interesting, as Mr. Spock is wont to say. If this curves a bit north I expect to be “sprouting antennas in an emergency” once again. This could cause more than a few problems, based on the last bit of rough weather last month.

    Have you been able to set up any sort of just-in-case radio equipment in Irvine?

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