Bob Henson ·

Above: Terra/MODIS visible satellite image of Hurricane Ophelia from Saturday, October 14, 2017. The Azores are outlined at center top. Image credit: NASA/EOSDIS WorldView.

The 2017 Atlantic hurricane season continued to astound on Saturday morning with the unexpected ascent of Hurricane Ophelia to major-hurricane status. Based on a very impressive satellite signature, the NOAA/NWS National Hurricane Center brought Ophelia’s peak winds up to 115 mph at 11 am EDT, making it a low-end Category 3 storm. The wind estimate may be conservative, said NHC forecaster Lixion Avila in the NHC forecast discussion. Ophelia was located about 220 miles south of the Azores, moving northeast at 25 mph. Ophelia is expected to pass within 100 miles of the Azores’ southeasternmost island, Santa Maria. The island will be on the hurricane’s weaker left-hand side, but winds could reach tropical-storm force, and squally weather is likely. Much bigger impacts from Ophelia are expected in Ireland (see below).

Figure 1. A remarkably well-organized Ophelia in enhanced infrared satellite imagery from 1:45 pm EDT Saturday, October 14, 2017. Image credit: NOAA/NESDIS.

To call Ophelia unusual would be an understatement. For one thing, it became a major hurricane at longitude 26.6°W, further east than any other formation of a Category 3 in the Atlantic. The former record-holder was Frances (1980), which became a Category 3 at 12.8°N, 29.8°W. Ophelia’s achievement is even more impressive when you consider its latitude: 34.8°N. In data going back to 1851, no other major hurricane is known to have formed anywhere close to as far northeast as Ophelia. The runner-up at Ophelia’s latitude range, Michael (2012), developed some 900 miles further west (see Figure 2 below).

Ophelia also extends this year’s count of major Atlantic hurricanes to six, a tally last achieved in 2005. Only two years have notched seven major Atlantic hurricanes: 1961 and 2005.

Figure 2. Formation locations of all major hurricanes (Category 3 or stronger) in the NOAA database from 1851 though 2016. Hurricane Michael (2012) was the previous record-holder for easternmost major hurricane formation in the 30°-40°N latitude range. Image credit: Sam Lillo (University of Oklahoma) and Philippe Papin (University at Albany, SUNY).

What’s a major hurricane doing in a place like this?

By conventional standards, one wouldn’t even expect Ophelia to be a hurricane, much less a major one. Sea surface temperatures beneath Ophelia are around 25°C (77°F), which is roughly 1°C below the traditional benchmark of SST levels warm enough to support tropical development. However, these waters are about 2°C (3.6°F) above average for the location and the time of year, and upper-level temperatures near the top of Ophelia are several degrees C below average. The result is enough instability to support well-organized showers and thunderstorms (convection), even though the convection is less intense than it would be in a warmer environment. A 2015 study led by Ron McTaggart-Cowan (Environment Canada) showed that a better threshold for systems like Ophelia that are transitioning away from the tropics would be based on potential instability between lower and upper levels of the hurricane, rather than on SSTs alone. Ophelia meets this threshold, according to Philippe Papin (University at Albany, SUNY).

Other things are also working in Ophelia’s favor. A strong outflow jet at upper levels on Ophelia’s west side is helping to ventilate the hurricane, and the 12Z Saturday run of the SHIPS model showed that wind shear on Saturday was in the light to moderate range (about 10 – 15 knots). The shear will begin to increase rapidly by Saturday night, heralding a change to come in Ophelia’s structure.

Figure 3. Probability of tropical-storm-force winds (sustained at 39 mph or more) along Ophelia’s track. The probabilities exceed 50% over all of Ireland and Northern Ireland and are as high as 90%+ in southwest Ireland. Strong winds may sweep across Scotland as well. Image credit: NOAA/NWS/NHC.

Ireland braces for a major windstorm on Monday

With Ophelia strengthening even more than predicted, a destructive windstorm in Ireland on par with some of the most damaging in the nation’s history is becoming increasingly likely. This weekend, Ophelia will be picked up by an approaching upper-level trough and will accelerate east-northeast and then north-northeast. As it does so, the hurricane’s structure will take on more and more characteristics of a very powerful midlatitude winter-type storm, although it’s possible Ophelia will retain an eye-like feature as part of what’s called a warm seclusion. Models strongly suggest that the upper-level dynamics will be potent enough to bring Ophelia’s central pressure by Monday to an even lower value than the 960 mb reported in NHC’s 11 am EDT Saturday advisory.

Regardless of whether it is still classified as a hurricane or not, Ophelia is predicted to approach Ireland on Monday with top winds somewhere near hurricane strength, plus an expanding field of gale-force winds. Our top track models are in close agreement that Ophelia’s center will sweep along or near Ireland’s west coast on Monday, putting most of the country on the storm’s more dangerous right-hand side. The GFS model has a particularly worrisome track, bringing Ophelia squarely across western Ireland and onward as a rapidly weakening storm through Northern Ireland and Scotland.

Figure 4. The 12Z Saturday run of the GFS model predicts that Ophelia will be at the southwest tip of Ireland at around 1 PM local time (12Z) on Monday, October 16, 2017. The central pressure of 958 mb would be even lower than its central pressure on Saturday morning, October 14. Winds shown are in knots; multiply by 1.15 for miles per hour. Image credit: tropicaltidbits.com.

As Ophelia reaches Ireland, we can expect winds of 50 – 70 mph to be slamming into Ireland’s southwest coast, and sustained winds of 40 – 50 mph will likely extend well inland. One concern for Ophelia’s impact on Ireland may be the potential for the ex-hurricane to develop a “sting jet”. This is a current of extra-strong jet stream winds that start out about 3 – 4 km above the surface, then descend over a 3 – 4 hour period. Rain falling into the jet evaporates and cools, causing the winds in the sting jet to accelerate as they reach the ground.

Ophelia is expected to complete the transition to an extratropical storm just off southwest Ireland on Monday morning. As this process unfolds, the wind field of Ophelia will expand, and Ophelia promises to be a damaging wind event for Ireland. Expect widespread tree damage and uprooted trees, damaged roofs, power blackouts, mobile phone coverage interruptions, and flying debris. Met Eireann, the Irish meteorology service, has a “status red” alert in effect for the southwestern counties of Galway, Mayo, Clare, Cork and Kerry, where sustained winds above 80 km/hr (50 mph) and gusts topping 130 kph (80 mph) are expected. Ireland’s National Emergency Coordination Group will meet on Sunday to discuss storm preparation, according to the Irish Times. The UK Met Office is warning of possible power loss and building damage across Northern Ireland.

There may be coastal flooding from Ophelia’s high surf and battering waves, and localized storm surge is possible, but Ophelia’s rapid motion will help limit the surge threat, according to storm-surge expert Dr. Hal Needham.

Ophelia could bring up to 2” of rain over higher terrain in Ireland. Heavy rains from a decaying Ophelia (perhaps 2” or more) may extend all the way to western Finland.

Hurricane history of the UK and Ireland

We don’t often talk about Europe when discussing hurricanes, and Ophelia is likely to be one of the top ten most notable Atlantic ex-hurricanes to affect Europe over the past 50 years. Hurricanes that transition to powerful extratropical storms hit the UK or Ireland several times per decade, on average. Some recent examples:

The extratropical version of Hurricane Katia skirted the northern coast of Scotland on September 12, 2011, two days after transitioning from a hurricane to an extratropical storm south of Newfoundland, Canada. According to Wikipedia, a maximum wind gust of 158 km/h (98 mph) was recorded on Cairn Gorm, Scotland as Katia impacted the region, with a peak gust of 130 km/h (81 mph) observed at a non-mountain station in Capel Curig, Wales; these observations marked the strongest impact from a tropical cyclone since Hurricane Lili in 1996. Waves up to 15 meters (49 ft) battered the western coastline of Ireland, and fallen power lines temporarily disrupted DART services. Approximately 4,000 households were left without power across the country. A catering marquee was blown into the air on a set for the television series Game of Thrones, causing one injury. In County Durham, United Kingdom, a man was killed after a tree fell on the minivan he was driving. Damage estimates in the United Kingdom alone topped £100m ($157 million 2011 USD). The remnants of Katia produced damage as far east as Estonia and Russia. In St. Petersburg, wind gusts up to 45 mph (75 km/h) damaged buildings and left roughly 1,500 residents without power.

Figure 5. Waves break over the sea wall along Portstewart harbour in Portstewart, Northern Ireland, as the remnants of Hurricane Katia hit the British shores, on September 12, 2011. Image credit: Peter Muhly/AFP/Getty Images.

Extratropical storm Bill of 2009, which hit Ireland on August 25 with sustained winds of 45 mph, had been a Category 4 hurricane northeast of the Lesser Antilles five days prior. Bill brought heavy rain and severe gales to the UK.



Extratropical Storm Alberto of 2006, which had been a strong tropical storm that hit the Florida Panhandle, hit northern Ireland and Scotland as an extratropical storm with 35 mph winds.



Extratropical Storm Gordon hit Ireland on September 21, 2006, with sustained winds of 65 mph. Gordon brought record warm temperatures as tropical air pushed north across the UK, and also strong winds that brought down power lines in Northern Ireland. Wind gusts to 60 mph (97 km/h) occurred in the Isles of Scilly off the southwest coast, and 81 mph (130 km/h) on the mainland.



Extratropical Storm Helene hit northwestern Ireland on September 27, 2006, with sustained winds of 45 mph.

Extratropical Storm Lili moved across Britain on October 28 – 29, 1996. Ex-Hurricane Lili brought gusts in excess of 90 mph, and caused widespread impacts across the UK and significant disruption.

There is officially one fully tropical hurricane that has hit Europe: Hurricane Debbie of 1961, which tracked through the western Azores as a Category 1 hurricane, then arced northeast and brushed the west coast of Ireland on September 16, also as a Category 1 hurricane. However, there is evidence that Debbie transitioned from tropical to post-tropical (extratropical) cyclone before hitting Ireland (see also this discussion at Irish Weather Online). Debbie passed close enough to Ireland to produce major destruction. Wind gusts reached 106 mph at Ballykelly and 104 mph at Tiree and Snaefill, and coastal radio stations reported the airwaves were jammed with calls for help from small ships and fishing craft. Eleven people were killed and 50 injured in the storm. The only other tropical cyclone recorded to have hit Europe since 1851 was Hurricane Vince of 2005, which hit southern Spain as a tropical depression on October 11, 2005. Historical documents also suggest a hurricane hit Spain on October 29, 1842.

Sunday, October 15, 2017 is the 30th anniversary of one the most talked-about weather events in UK history, the ‘Great Storm’ of 1987. See the UK Met Office article on this weather event, whose 100-mph wind gusts killed 22 people and caused around £1 billion worth of damage. It has gone down in history as one of the worst UK storms since 1703 and will obviously be remembered for Michael Fish’s now-legendary television broadcast.

Figure 6. Infrared GOES-16 satellite image of 92L at 2:00 pm EDT Saturday, October 14, 2017. Image credit: NASA/MSFC Earth Science Branch. GOES-16 images are considered preliminary and non-operational.

92L near the northern Leeward Islands may affect Bermuda next week

A disturbance near the northern Leeward Islands on Saturday, dubbed 92L, could become the Atlantic’s next tropical cyclone next week, although the odds are mostly stacked against it. SSTs of 28-29°C (82-84°F) are more than warm enough for development, and the environment around 92L is sufficiently moist (mid-level relative humidity around 60-65%). Wind shear is strong, though—around 25 knots—and the shear is expected to remain in the 20 – 35 knot range throughout the next five days, according to the 12Z Saturday run of the SHIPS model. In their 0Z Saturday runs, none of the GFS ensemble members develop 92L, and only about 10-15% of the European ensemble members produce a tropical storm from it. If 92L does develop, it could track near Bermuda around Tuesday or Wednesday as a depression or weak tropical storm. Before then, 92L will bring scattered showers and thunderstorms to the hurricane-hammered northern Leeward Islands over the weekend and to Puerto Rico on Sunday and Monday.

California’s prolonged fire calamity

The death toll has risen to 35 from the ongoing week-long fire disaster in California, and fire weather continues to be problematic this weekend. See our Friday evening post for more details. We’ll be back with a new post by Sunday afternoon.

Dr. Jeff Masters contributed to this post.



