Rain of Terror: An Atmospheric River, Ex-Typhoons, and the Tropical Connection

Well Van, what a difference a week makes, but thanks to modern day weather prediction we saw this change coming 7-10 days in advance. On a post back on October 9th, I discussed the potential for a fairly significant mid-week storm for the BC coast this week.  

Solander Island will take the brunt of the wind Thursday afternoon and evening

Solander Island will take the brunt of the wind Thursday afternoon and evening

Some of our most advanced forecasting guidance caught on to this potential storm event back on the evening of October 8th, or over 192 hours in advance. Wind gusts near the headlands of Vancouver Island will gust over hurricane force Thursday (tomorrow) evening, especially over Brooks Peninsula. I'll often check Solander Island weather conditions during strong wind events, as these unmanned weather station often reports the strongest winds.

Don't worry, it's uninhabited.

Here is a look at some advanced ensemble forecasting output generated on October 8th showing the immense amount of time before tomorrow's storm.

NAEFS showing the 8 day advanced notice to this moderate wind/rain storm poised to hit the West Coast

NAEFS showing the 8 day advanced notice to this moderate wind/rain storm poised to hit the West Coast

Rain totals over the next 120 hours will be quite significant for the B.C coast, with communities such as Tofino and Bella Bella receiving in excess of 200 mm over the next 5 or 6 days, as shown below:

Note the intense orographic influence on the west side of Vancouver Island, and the obvious rain shadow along the inner South Coast. Most of the precipitation is 'rained out' before it makes its way over the Rocky Mountains 

Note the intense orographic influence on the west side of Vancouver Island, and the obvious rain shadow along the inner South Coast. Most of the precipitation is 'rained out' before it makes its way over the Rocky Mountains 

The synopsis

A stationary low is currently churning in the Gulf of Alaska, but the real weather story will be a strengthening front and developing low pressure system tracking in from the southwest bringing a skirt alert to most exposed coastal sections around southern British Columbia. Communities such as Comox and Campbell River should prepare for very isolated power outages Thursday evening as sustained winds will be between 30-40 knots over Georgia Strait with higher gusts possible (70-90 km/hr) 

Wind warnings are possible for portions of the BC coast, especially West Vancouver Island and portions of northern Georgia Strait 

Wind warnings are possible for portions of the BC coast, especially West Vancouver Island and portions of northern Georgia Strait 

The developing low does an excellent job at drawing some subtropical moisture out of the lower latitudes, which is adding to the amount of rainfall forecasted for Tofino and other coastal locations. Precipitable Water may sound like a tricky foreign concept or just more weather jargon, but think of it like this: Imagine wringing out the clouds/atmosphere (like a towel). The amount of moisture that falls to the surface can be quantified as precipitable water. Typically regions with higher precipitable water values receive higher amounts of precipitation. 

A new low pressure system developing for Thursday advects some moisture from the southern latitudes. Note: Hurricane Ana approaching Hawaii on the bottom portion of the diagram

A new low pressure system developing for Thursday advects some moisture from the southern latitudes. Note: Hurricane Ana approaching Hawaii on the bottom portion of the diagram

During the early morning hours of March 12th, 2012 significant storm surge occurred on eastern portions of Vancouver Island closing numerous coastal roads and causing significant coastal erosion PIcture: Campbell River BC 'Big Rock' the morning of March 12th.

During the early morning hours of March 12th, 2012 significant storm surge occurred on eastern portions of Vancouver Island closing numerous coastal roads and causing significant coastal erosion PIcture: Campbell River BC 'Big Rock' the morning of March 12th.

The BC Storm Surge Forecasting Program model indicates very modest increases in sea heights of about 30 cm for southern BC, fairly non-significant. Potent west coast lows can wreak havoc along portions of the coast especially when they hit during high tide. The March 12th, 2012 storm is a great example of a deep low pressure system hitting during high tide. 

Thankfully this low pressure system is much weaker and will bring modest changes in sea heights to coastal regions of B.C

Storm Surge Forecast for early Friday

Storm Surge Forecast for early Friday

On the weekend, the remnant energy from Typhoon Vonfong will arrive on coastal B.C bringing another bout of gusty winds and heavy rains.

Sound like a broken record, yet?

Tropical Tidbit

Tropical Storm Ana (Yes, it's an A because we've already been through the alphabet once in the eastern Pacific) is forecasted to gradually strengthen and become a weak hurricane as it tracks closer to the Hawaiian Islands. Hurricane watches will be likely be issued later tonight or tomorrow for portions of Hawaii, and all islands will at least be directly affected by this storm.

Heavy, flooding rains will be the greatest threat, mainly because the system will be a slow mover. It will take in excess of 48 hours to clear the Hawaiian Island Chain.

Numerous weather models indicating this storm poses a moderate threat to Hawaii.

Numerous weather models indicating this storm poses a moderate threat to Hawaii.

As far as landfalls are concerned in Hawaii, they're truly few and far between. After doing some digging only Hurricanes Dot of 1959 and Iniki in 1992 have made direct landfalls. Current model consensus, including the National Hurricane Centre's preferred path indicates the storm is most likely to skirt just south of Hawaii. In fact, the Big Island has never had a hurricane make landfall See for yourself (Courtesy Meteorologist Mark Nelson):

NHC current projected path, forecasting a near miss for the Big Island. Heavy rains will still be a great concern

NHC current projected path, forecasting a near miss for the Big Island. Heavy rains will still be a great concern

How much rain is forecasted with this system?

Hurricane rain model, indicating extremely torrential rains for portions of the Hawaiian island chains especially Big Island, with above model showing a casual THREE FEET (90 cm +) of rain. Observed amounts will likely be less. 

Hurricane rain model, indicating extremely torrential rains for portions of the Hawaiian island chains especially Big Island, with above model showing a casual THREE FEET (90 cm +) of rain. Observed amounts will likely be less. 

After Ana weakens and begins to turn NW it will eventually become extra-tropical and re-intensify down the road. The latest GFS run (18Z on Wednesday) suggests it may attempt one of the greatest squeeze plays of all time, sneaking between 2 significant high pressure systems - Don't bet the farm, though.

Middle of next week, much uncertainy remains to where extra-tropical Ana will end up. Anyone's guess as of right now

Middle of next week, much uncertainy remains to where extra-tropical Ana will end up. Anyone's guess as of right now