This is a complex storm. Three different elements are coming together. A northern jet, a southern jet, and Tropical Storm Phillipe. The result appears to be tropical storm to hurricane force wind gusts, heavy rain, and coastal implications for Maine Sunday night into Monday.
The Surface Wind
As I have discussed on the Pine Tree Weather Facebook Page, the most concerning aspect of this storm will be the wind factor. There is all kinds of gloom and doom wind graphics being spread around social media. While it is true that the wind will be hurricane force strong at low altitude, the question remains is how much of the high speed wind makes the surface. The National Weather Service Gray office agrees in its Saturday afternoon area forecast discussion:
And indicator of what all of this means is here:
What is displayed here is horizontal view of the atmosphere for Portland and Bangor. The wide yellow line indicates the mixing layer height. For Portland, it only shows a very narrow window for 60 knot gusts, displayed in pink. Bangor is a different situation with about a three hour window for 60 knot gusts. The Penobscot Bay area appears to be a target for the strongest, prolonged area of wind gusts. Models have targeted that region fairly consistently since Thursday. That idea is present in the Saturday 12z ECMWF (Euro) model run:
The greatest threat for the most damaging wind gusts range in the 4 AM to 9 AM time frame for western and southern areas, and from 8 AM to 1 PM for eastern and northern areas. Gusts 40-50 mph range will continue in both areas well into the afternoon. With a front approaching on the heels of the storm and high pressure trailing behind, a strong breeze is expected to continue well into Tuesday.
If the wind from the storm isn’t enough, the threat of downdraft wind in heavy rain and thunderstorms is another issue to contend with.
Rainfall, Straight Line Wind and Flood Potential
Vertical velocity, shown above, is upward motion. This is a common feature in thunderstorms and anything tropical. This model idea indicates a high level of action at the 700mb level (10,000 feet) in the atmosphere. What this means is the threat for heavy rain, and for potential downdraft wind.
This makes the wind concern a two tier concern: surface wind, and straight line wind. With the low level jet stream well over hurricane force at the 850mb level (5,000 feet) the rain falling through the atmosphere, if heavy enough, could bring that wind down to the surface. The greatest area of concern for that is the mountains and foothills of western Maine.
Not only that two tier wind threat a problem for western areas, the flood threat is there also:
The Northeast River Forecast Center has picked up on this idea. Given the amount of rain that could fall with this storm, potential is there for river flooding. The recent rain has increased river levels, and another 1-3″ with localized higher amounts in downpours and thunderstorms could cause problems in some areas.
The Swift River in West Roxbury is a rather consistent flooder when heavy rain is in forecast. The NERFC is already predicting potential minor flooding issues. Anyone who lives near streams and brooks should monitor levels closely, and be prepared to take quick action in case of fast rising waters.
As with the last storm, clogged storm drains from leaf drop could cause urban street flooding. Ponding on roadways could cause potential hydroplane issues.
This is a graphic merging the two National Weather Service office ideas for total rainfall as of Saturday afternoon. A good portion of the state can expect at least one inch of new rainfall, with the higher end amounts over the higher elevations of western areas. This a general idea, localized amounts may vary due to potential dry slotting on the low end, and downpours on the high end. Overall, 1-3″ is expected.
The timeframe for rain is for it to begin Sunday afternoon over western areas expanding over the state in the evening. Heavier rain impacts southern and western areas by around 1 AM to 8 AM Monday, northern and eastern areas from around 5 AM to noon. Showers end for southern areas around noon, northern areas by evening.
It’s a good thing that astronomical tides will not be an issue with this storm. The current moon phase is waxing gibbous at nearly three-quarters full. There are potential problems, however. There is a high tide to contend with at the height of the storm for the southwest coast on Monday.
Portland’s high water mark as the graphic displays is nothing would indicate any concern.
For the DownEast coast, this is just an ordinary day under normal circumstances.
What makes it concerning is the intensity of the wind of the storm from the south / southeast pushing water toward the shoreline. There is potential for a 1-2 foot storm surge in the hours leading up to high tide. The ocean will be plenty ugly as the National Weather Service Gray marine forecast indicates 15-20 foot seas at the high water mark. The National Weather Service Caribou marine forecast is also on board with that idea. Storm warnings have been posted by both offices for the entire Maine coast. Some beach erosion and high waves could impact the shorelines from 5-9 AM Monday.
Prepare For Power Outages… And Surprises
Given the complex nature of this event that I have outlined in this post, there is plenty of wind to be concerned about, and many moving parts associated with it.
Given the nature of a southeast wind direction, there is threat for tree damage. The root structure of the trees in the region are girded against southwest to northeast winds. A strong southeast wind event is rare one, especially of this magnitude. With the recent rains helping to anchor the soil, the threat could be reduced somewhat, but with the strong gusts anticipated, it could cause problems. In an nutshell, it would be wise to prepare for power outages.
With the three elements at play of the merger of the major jet streams and the added influence of Tropical Storm Phillipe, the surprise factor of the unexpected could occur. Please stay updated with the National Weather Service forecasts, and make sure you are following Pine Tree Weather on Facebook.
Always Stay Weather Aware!