Spaghetti Plots…Storm Approaching Hawaii

October 14, 2014

Tropical Storm Ana is revving up and should become a hurricane within 24 hours.  This storm is forecast to end up somewhere over or quite close to the main Hawaiian Islands.  If a landfall actually happens, as far as I’m aware it will be unprecedented in historical times.  Here is a map showing all the storms that have passed within 75 miles of the main island chain…not as many as you would think:


Of course there is always error, especially 4 days out.  The official CPHC forecast looks like this right now:

MarkTropical_HurricanePacific MarkTropical_HurricanePacific2

But you might find this more interesting…a loop showing all the different model forecasts for where the center of the storm will go.  Each line is one model.

Interesting stuff eh?  Shows you why the forecast track can be so uncertain and also why it’s so important to not focus on a specific track in the middle of the “forecast cone”.  And you can also see why we call these types of charts “Spaghetti Plots”!

So as of right now it might not be a big deal, or it might be a huge storm.  For it to be a big storm, the center has to hit one of those little dots of land!

Chief Meteorologist Mark Nelsen

How Windy Tomorrow? Not a Storm, But Windy

October 14, 2014

We stayed mainly dry in the metro area today since the main rain band with a cold front has been just to our south.  We figured it would be right over us instead.  Nice way to bust a forecast though!

You may have heard rumblings of strong wind coming tonight or Wednesday.  Here’s the latest:

  • A windstorm is not on the way
  • But gusty southerly wind will develop across the western valleys of Oregon/SW Washington and the coastline late tonight and then die down after mid-morning tomorrow
  • Peak gusts 30-35 mph are likely for most of us.  About 5-10 mph stronger than last night’s gusts.
  • 40-45 mph at the Coast
  • This is strong enough for a few limbs to fall since most leaves are still on the trees, of course there will be a few scattered outages.

The NWS issued a Wind Advisory earlier this afternoon for peak wind gusts around 40 mph in the central/north Willamette Valley tomorrow morning.  I think that’s a bit much and 40 mph gusts are a bit high.  I bet PDX ends up with a peak gust 30-35 mph at best.  That said, 30-35 mph gusts in mid October will easily bring down some branches…and lots of leaves!  That means some scattered power outages are possible again like this morning.

Where is the wind coming from?  A surface low or open wave will scoot quickly north along the coastline later tonight and tomorrow morning, giving us the rush of air behind it from the south.  Models are in some disagreement on how much wind we get (lowering my confidence that anything interesting will even happen!).  The NAM has no strong wind at all, the HRRR shows no gusts over 30 mph (or even less) in the Valley:


The ECMWF gives a little more energy to the wave in the afternoon, which means no closed low and not much wind in the morning.  The WRF-GFS is alone showing wind gusts maybe 35-40 mph late tonight and early tomorrow:


Our RPM model looks like this:


That would imply gusts close to 40 mph, but our model almost always is too high…note the text output


With most wind events you can assume this text output is 5-10 mph too high on gusts, so this tells me not much is going to happen tomorrow other than the effects I noted above.

Chief Meteorologist Mark Nelsen