Arthur 'guaranteed' to hit the Maritimes

Friday, July 4, 2014, 8:35 AM - It’s a guarantee that Arthur will hit the Maritimes on Saturday. While it won’t likely be a true hurricane by the time it approaches the south shore of Nova Scotia, the storm will be mutating into a powerful ‘post-tropical’ system with elements of a hurricane and nor’easter.

Arthur, the mutant storm

Here’s what will happen. Regardless of how strong Arthur gets while over the warm waters of the gulf stream near North Carolina, its small inner core where the strongest winds are located will begin to breakdown as the storm moves over colder waters late Friday.

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As this happens, Arthur will also begin to merge with an upper level trough (dip in the jet stream) overnight Friday into Saturday morning. The storm will effectively be mutating from a tropical system into something that looks more like a nor’easter. The maximum sustained winds will not be as strong once the inner core dissipates, but the merger with the upper level trough will serve to keep the overall system strong and actually cause it to grow in size.

What it means 

Rain: There is high confidence that the heaviest rain will fall in New Brunswick to the west of where the centre of low pressure tracks. In excess of 100 mm is possible which would lead to flash flooding. At this point, Saint John, St. Stephen and Fredericton appear to be in the target zone for the heaviest rainfall and are at greatest risk for flooding.

The heavy rain will begin well ahead of the storm centre. Scattered showers and thunderstorms are possible through the day on Friday, with the main rain shield from Arthur and heaviest rain falling overnight Friday into Saturday morning. The rest of the Maritimes will likely see some brief periods of heavy rain, but only extreme southwest Nova Scotia and western PEI have a real chance for serious rainfall.

Wind:  It’s likely that the inner core of Arthur will fall apart before it makes a landfall around the south shore of Nova Scotia or the Bay of Fundy. However, there will be a large and strong wind field around the storm, particularly on the south and east side. This means Nova Scotia is in line for the strongest winds.

Baccaro Point in Shelburne County is a good candidate to see the highest sustained wind and gust. Halifax will see strong southeast winds to start the day but they will quickly turn to be strong and gusty westerlies by the afternoon. The winds across New Brunswick and PEI will be strong as well, although somewhat less intense than over Nova Scotia.

Impact: No two storms are the same, but the track and intensity of Arthur looks very similar to Earl in 2010. 

Earl was a borderline tropical storm/hurricane when it made landfall along the south shore of Nova Scotia. It maintained a tropical look for longer than what Arthur is likely to, but the intensity of winds is likely to be similar. This would mean widespread power outages across Nova Scotia from fallen tree limbs, but not widespread infrastructure damage like what was seen with Hurricane Juan. While the wind will not be as strong in New Brunswick and PEI, very heavy rain combined with gusty winds could be enough to cause some power outages. Flooding will be a major concern in New Brunswick, particularly for any low-lying areas prone to water problems. Arthur will have mutated almost completely into a nor’easter type storm by Saturday night as it moves into Newfoundland. While unsettled and stormy in places, it is not expected to cause the same level of disruption as in the Maritimes. Conditions will improve dramatically for the Maritimes on Sunday with a generally fair, warm and breezy day in store.