Mountain Snow Season Arrives Friday, Eta To Bring Catastrophic Flooding To Nicaragua/Honduras

We had the best Halloween weather in 95 years and stunning weather today, and Monday will be another beautiful day with only a few high clouds increasing late in the day. But by Tuesday morning, the first of several systems this week will bring rain to the area, and on Friday, we’ll see a shift to northwesterly flow, giving us cooler and wetter-than-average weather and allowing snow to build up in the Cascades. I’ll cover our weather during the latter half of this blog, but the first half will be dedicated to the tropics, far away from US soil.

Typhoon Goni

Typhoon Goni made landfall at 4:50 am local time Saturday at Catanduanes Island Province in the Philippines. Goni reached peak strength at landfall, and was estimated to have 195 mph sustained winds at landfall. If this estimate holds, it would make Goni the strongest landfalling cyclone on record by measured wind speed.

#TyphoonGoni made landfall @ 4:50 am local time Saturday at Catanduanes in the Philippines with estimated 195 mph sustained winds, which would make it the most intense landfalling cyclone on record by wind speed.

Satellite credit: CIRA, retrieved from Typhoon Goni Wikipedia page pic.twitter.com/Q6pb1qpBdR

— Charlie Phillips (@GeoduckChuck) November 1, 2020

Thankfully, Goni only grazed the capital of Manila, home to nearly 14,000,000 people (per 2020 census). So far, there have been 10 fatalities from the storm. Typhoon Haiyan in 2013, another extraordinarily powerful typhoon with 190 mph winds at landfall, caused catastrophic damage to the populated Visayan Islands, killing at least 6,300 and leaving nearly 2 million Filipinos homeless.

The Western Pacific is the most active tropical cyclone basin, and the Philippines alone average an incredible 20 typhoons per year. For reference, the entire Atlantic Basin sees an average of only 10 named storms each year. The storms in the Western Pacific also tend to be stronger – 41 storms in the Western Pacific have seen pressures under 900mb, while only 5 storms in the North Atlantic have. This is simply because the Western Pacific has more favorable conditions for cyclone formation and strengthening than the Atlantic, and it has them over a wider area.

Tropical Storm Eta

But the Atlantic is certainly no slouch in the hurricane department, especially this year. And hot on the heels of Hurricane Zeta being the record 5th hurricane of the year to make landfall on the Louisiana Coast, high-end Tropical Storm Eta is strengthening over the northern Caribbean and is expected to make landfall along the NE Nicaraguan Coast Tuesday morning as a major hurricane.

Unlike Zeta, which moved extremely quickly and brought hurricane-force winds well inland but relatively little rainfall, Eta will move very very slowly inland and could cause catastrophic flooding in addition to extreme winds. It is located in a favorable environment for intensification with low wind shear, deep moisture, and very warm sea-surface temperatures, so the slower it moves, the stronger it should become. And if it stalls just off the coast on its way inland, it will direct extremely heavy bands of rain into Nicaragua and Honduras while maintaining its strength.

The model below shows Eta making landfall Tuesday night as a Category 3 storm with 125 mph winds. This seems like a reasonable forecast, but if the storm stalls offshore even a little bit, it easily strengthen to a Category 4 given the favorable conditions.

Here are the GFS “spaghetti plots” showing the track and strength of Eta. Note how much uncertainty there is in track – and therefore strength, though all models show Eta strengthening significantly before landfall. The labeled strength (ex: 993 mb at hour 24) is the average of all the storm tracks at that point and is not a forecast for the actual minimum low pressure of Eta during that time. Not all models show the turn to Cuba (and potentially the US) and while it is something to keep in mind, my eyes will be on Nicaragua and Honduras this week.

Comparison to Hurricane Mitch

The whole situation has shades of Hurricane Mitch this time of year in 1998, which caused over 11,000 fatalities primarily in Honduras and Nicaragua when the storm moved very slowly inland and caused catastrophic flooding/mudslides over the two countries.

I hate to even mention Mitch and I don’t want to fearmonger – I’m not saying Eta will be equivalent, just that it has similarities. Still, looking at this forecast raises a lot of “alarm bells” in my head and I fear that this could be a catastrophic flooding event. Fingers crossed the worst-case scenario does not come to fruition.

Pacific Northwest Forecast

Thankfully, I have some good news for the rain fans of the Pacific Northwest! After one more splendid day of sunshine on Monday, we’ll see increasing clouds Monday night and rain arriving Tuesday. The system can be seen in the satellite image below as the band of clouds approximately 1000 miles off the West Coast.

Precipitation will begin late Monday night for the Northern Washington coast and should reach Western Washington shortly before sunrise. Portland should see rain beginning midday, but rain will be far weaker here than points to the north.

Expect a few afternoon showers before another weak, trailing front (visible as the band of precipitation near 135W in the graphic above) moves inland overnight. On Wednesday, a moderate/strong system should head towards British Columbia, bringing gale force winds and 15-20 ft seas off the NW Washington Coast and moderate rain to Western Washington while NW Oregon remains merely breezy and dry.

Things become a bit more interesting Thursday and Friday. Thursday could be very wet as a diffuse but moist system moves inland, and on Friday, a deep upper-level trough will arrive from the NW, bringing cool, moist onshore flow and the first major snowfall of the season for the mountains. Snow levels will be in the 6000-9000 foot range through Wednesday and will only drop to 5,000 feet on Thursday, but Friday’s system will drop snow levels below the passes and could create travel difficulties for those heading over the Cascades.

We’ll dry out and cool down for the weekend as this trough moves over the area with highs in the upper 40s. We look to return to cool NW flow next week with below-average temperatures and slightly-above average precipitation. This is a textbook La Nina pattern and hopefully one we’ll be seeing a lot more of this winter!

Have a great week and enjoy the last day of sunshine tomorrow! And don’t forget to vote if you haven’t already 😉
Charlie