Italy has seen its fair share of rainfall this past week, especially in the northern tier of the country including the city of Milan. Trouble started off in early November when a system originating from the Mediterranean Sea brought abnormal amounts of moisture into the region, producing heavy rainfall over a sizeable portion of Italy. This system, associated with a slow moving negatively tilted trough, dug down into southwestern Europe and triggered isolated thunderstorms and widespread rain. The system dumped copious amounts of rainfall – over 100mm fell in northern parts of Italy. With already saturated grounds from previous events in the past few weeks, this meant trouble for some villages.
Milan and surrounding areas saw the worst of the flooding. Subway systems were inundated with water, streets were flooded with over a foot of water and schools were forced to close. Two rivers in the region, the Seveso and Lambro, overflowed their banks and contributed to the flooding. The flooding is responsible for five deaths and estimated damages in excess of 100 million dollars.
Significant repairs will have to be done to this central Milan canal wall and road which collapsed due to the saturated ground below that gave way. (Source: @SimoneEneaRicco)
Northern Italy will remain soggy over the weekend, with another 10-20mm expected due to the same slow moving trough which continues to linger. Throughout November Milan usually sees about 100mm of precipitation, but just half-way through they have already surpassed it.
By the beginning of next week there’s a good chance that things will start to clear up as a weak ridge builds in.
Super Typhoon Nuri Transitions into Strong Extratropical Storm
The Western Pacific continued to be active this past week, spinning up yet another violent storm, which thankfully remained at sea and did not impact land. Nuri formed late last week west of Guam and slowly drifted west-northwest. It organized itself as conditions became ideal for strengthening of the typhoon: sea surface temperatures were very warm and wind shear was low. Nuri became a super typhoon last weekend as it deepened to a central pressure of 910mb and brought estimated sustained winds of 285km/h – similar conditions to what super typhoon Vongfong had at its peak this past October. Up to date, these two are tied for the strongest tropical storm of 2014. Nuri quickly curved Poleward before reaching Japan, sparing the Japanese islands from the storm.
IR satellite image of Nuri as it held super typhoon strength this past Sunday/Monday. (Source: Soumi NPP VIIRS)
Nuri did not end there, however. As it got captured by the polar jet stream, it transitioned into an extratropical storm. Extratropical storms are the low pressure systems that we see across the mid-latitudes, including here in Manitoba. They have significant differences from their tropical brethren, the most significant being that extratropical storms have warm and cold fronts that generate energy for the storm, as opposed to tropical systems that have generally uniform temperature. As the remnants of Nuri transitioned into the Polar Jet they strengthened once again, aided by a strong temperature gradient aloft.[1] Projected wave heights on the Bering Sea neared 50 feet as the storm “bombed” out[2] on Friday to a minimum pressure of 927mb. Extremely strong winds were recorded on the Aleutian Islands, where gusts exceeded 150km/h.
Satellite picture of the remnants of Nuri as an extratropical storm on Friday.
The remnants of Nuri are expected to continue moving towards Alaska but weaken significantly by the time they reach the Alaskan shores, as the low pressure system enters its weakening phase.
Alaskan Bomb Results in Arctic Outbreak over Central & Eastern North America
The intense storm over the Aleutian Islands is also indirectly responsible for the outbreak of cold air expected in the coming week over much of North America. As the system intensifies over the Aleutian islands, a strong upper-level ridge will build over the west coast of North America which will cause a resultant upper level trough to deepen over the remainder of the continent.
The GDPS shows prominent ridging over the west coast of North America, resulting in a deep upper-level trough over central & eastern North America.
The deep upper-level trough will allow the cold air that’s been bottled up in the Arctic to spill southwards, resulting in well below seasonal temperatures across a significant portion of Eastern North America. The developing upper-level pattern is a fairly stable configuration for the flow, so no significant changes will likely occur in the next week or two other than gradual moderation.
The strong temperature gradient was easily evident by a very strong jet streak of over 130 knots – that’s over 240km/h – at 500mb! ↩
A system has “bombed” when its central pressure drops 24mb or more in 24 hours. ↩
The city of Vancouver has seen its fair share of rainfall this past week, causing flooding problems throughout the metro. What was to blame for this event was an atmospheric river that came onshore the BC Coast, aided by a large upper level trough off the West Coast on Wednesday. Atmospheric rivers are narrow plumes of significant moisture which originate from the subtropics and flow from the southwest onto the shores of the west coast. On Wednesday morning fairly high PWAT[1]
values (>1”), a product of the atmospheric river, nosed into the Vancouver region which set the stage for the heavy rainfall event.
Atmospheric river (high PWAT values) making its way onto Vancouver island. (Source: Twisterdata)
The rainfall started early Wednesday morning for Vancouver, including a thunderstorm that went through the city around 7am dropping heavy rain. With already saturated soil from the rain earlier in the week, flooding problems ensued. Metro Vancouver saw anywhere between 20-35mm, and pockets of locally higher amounts Wednesday. This event comes a day after the same system offshore brought very strong winds (gusts >100km/h) to Vancouver Island as well as downing power lines and snapping trees in metro Vancouver. It was reported that Tuesday night a total of 80,000 people in southern BC were without power at some time.
Flooding in Port Moody, just east of Vancouver, on Wednesday. (Source: Port Moody Fire Rescue)
As this mid-week system departs, it makes way for the next system upcoming system this weekend. This will be yet another fairly strong system to impact the west coast, bringing with it more heavy rains and strong northwest winds. Unfortunately, unsettled weather is expected to last for the Vancouver region into next week.
PWAT stands for precipitable water, a measure of the amount of water contained in a column of air. ↩
Another week, another tropical disturbance forms – this time in the Atlantic. Gonzalo started to organize earlier this week just east of the Caribbean and drifted west, slowly organizing itself at the same time. By the time it reached the eastern islands of the Caribbean such as Anguilla and the British Virgin Islands, Gonzalo was a category one hurricane and brought strong winds and heavy rains to the islands. Hurricane Gonzalo then started curving northeast and quickly strengthened into a category four, with a pinhole eye after it cleared the Caribbean Islands. The storm was then headed for Bermuda, which meant trouble for the small island out in the Atlantic.
Deep convection in the northern eye wall of Gonzalo depicted by the black colors. Bermuda is identified by the white arrow.
Gonzalo made landfall on Bermuda Friday evening, lashing Bermuda with high end category two winds (175km/h) as the eye wall made its way across the island. Reports of how Bermuda fared were difficult to find as of Friday evening, but it appears the island did quite well with no deaths or injuries reported. However, power was knocked out to about 90% of Bermuda’s residents as well as flooded streets reported. Compared to last week’s EIWN, the big difference is that the infrastructure in Bermuda is built to withstand fairly strong hurricanes, unlike most of the buildings in the region of India that Hudhud affected.
The Bermuda Weather Service launched a weather balloon as the eye approached Bermuda at 00z. (Source: University of Wyoming)
Hurricane Gonzalo will continue its trek northeastwards and may even clip Newfoundland by Sunday as it transitions to extratropical. Interestingly enough, Gonzalo will likely make it all the way to the United Kingdom as an extratropical storm early next week. No other storms are expected in the near future in the Atlantic.
