Weather Blog

It’s going to be a bit of a rainy weekend in Minneapolis-St. Paul this weekend. Hooray! The first batch of rain will arrive late this evening, giving way to a bit of a break tomorrow, followed by the threat for strong thunderstorms (though the heaviest storms will come south of Minnesota) on Saturday, and some lingering rain on Sunday. The area needs to be replenished, but of course, it is all coming on the weekend.

The above is satellite imagery from about 2 weeks ago, as a spiral band from Storm Daniel lashed the Libyan coast east of the Gulf of Sirte. Derna is one of the most northern points of that part of Libya, and suffered the most severe consequences of what was a virulent storm.

Daniel developed in the central Mediterranean, and started making headlines by bringing flooding rains to Greece, where Larissa, in particular, found itself underwater. This was caused by an Omega block, ridges of high pressure that orient the jet in the shape of the Greek letter Omega. This is a generally immobile pattern, and can cause short term drought beneath the ridge, and persistent rain on either side. Daniel wasn’t moving much, wobbling between the southern Balkan Peninsula and northern Libya.

The second accelerating factor was terrain of Libya in general, and the area near Derna, specifically. As you may know, Libya is dominated by the Sahara Desert. There is the Mediterranean climate in the northern coastal areas, so Derna and the other large cities of northern Libya aren’t foreign to rain, but it is pretty dry there, and significantly drier further to the south. It’s not soil that is receptive to rain falling at persistent or voluminous rates. It is prone to running off.

Pictured above is the 3d view looking north from Derna on Google Maps. There is a small river emerging from a network of canyons that cut deep into some cliffs. The entire topography of the region is set up to funnel runoff out of the desert through this canyon and out of Derna. There is a dam at the mouth of the canyon which allowed Derna to exist while also generating some electricity.

There WAS a dam, I should say. Under the onslaught of a cyclone’s worth of rain funneled through the canyon, the poorly maintained dam failed, unleashing all this water on Derna. Undoubtedly, years of dictatorial rule followed by a decade of civil unrest had led to poor civil infrastructure maintenance, and ultimately, tragedy.

As is often the case with the worst disasters, there was a perfect confluence of circumstances that made it so horrific.

There has been a little bit of positive news from the Atlantic, at least for Stateside interests. The track for Lee has turned a little bit to the right, away from New England and away from the Bay of Fundy, where it could have caused real problems. Instead, the weaker Tropical Storm Lee will land in southwestern Nova Scotia.

Surge and wind threats are lessened for the New England coast, and I’m not nearly as worried about amplified storm surge in New Brunswick, but tropical storm force winds are still going to be an issue for this area, even for parts of down-east Maine, which will get lashed by rain and tropical storm force winds, but the threat, at least in the States, will not be as severe or widespread.

Tropical storm force winds are still anticipated in the southern part of Nova Scotia and parts of coastal New Brunswick, but again, Lee is weakening, and it won’t be a hurricane making landfall in the Canadian Maritimes. The storm will make landfall around Yarmouth, Nova Scotia tomorrow morning, around 8am, CT, or 10 Atlantic time.

It’s been a long wait, and fortunately, Lee is looking like he showed his worst in the open ocean, and a bullet was almost dodged.