Category 2 Hurricane Ophelia was headed east-northeast at 12 mph late Friday morning towards the Azores Islands, and is likely to bring tropical storm-force winds and heavy rains to the Azores on Saturday, and to Ireland on Monday. Ophelia continued to look impressive on satellite imagery on Friday afternoon, with a distinct eye surrounded by a moderately intense area of heavy thunderstorms. Ophelia had favorable conditions to maintain hurricane strength, with moderate wind shear near 15 knots and sea surface temperatures (SSTs) a marginally warm 26°C (79°F)--about 1°C above average for mid-October.
#Ophelia has strengthened 20kt in last 24hrs. This type of intensification is rare in this region of the Atlantic pic.twitter.com/T3OziKTmkm
— Sam Lillo (@splillo) October 12, 2017
Ophelia will become caught in the prevailing westerlies this weekend, which will accelerate the storm to the east-northeast and then northeast. Sea surface temperatures will gradually drop and wind shear will rise on Saturday and Sunday, weakening the storm. However, Ophelia will begin to derive energy from non-tropical (baroclinic) processes this weekend, and should be able to maintain Category 1 strength until Monday, when it is expected to transition into a powerful post-tropical (mid-latitude) storm with winds of hurricane strength.
On Ophelia's expected course, the storm will track just south of Santa Maria, the southeastern-most island of the Azores, on Saturday night. The 12Z Friday run of the GFS model brings Ophelia within about 60 miles of Santa Maria. This track would put the island on the weaker left-hand side of Ophelia, where maximum sustained winds of 40 – 50 mph will be likely. In NOAA’s historical hurricane database, which extends back to 1851, only 11 hurricanes have passed within about 200 miles of the Azores (as noted by weather.com). Every one of those occurred in August or September—except for strikingly unseasonal Hurricane Alex, which struck the islands in January 2016 just after weakening to tropical-storm strength.
Figure 1. Wind forecast from the 0Z Friday run of the European model, valid at 18Z Monday, October 16, 2017. Sustained tropical storm-force winds of 65 kph (40 mph) were predicted along much of the southwestern coast of Ireland.
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. The Irish weather service has issued a Yellow Alert for Monday.
Winds will begin to strengthen in Ireland on Monday morning, but the real impact will be Monday afternoon and evening. Expect sustained southeasterly winds of 55 – 65 kph (34 – 40 mph) for coastal southwest Ireland (Munster province) and southeast Ireland (Leinster province.) Along the south Munster coast (south Cork and south Waterford), sustained winds of 65 - 75 kph (40 – 46 mph) are likely, and winds could be higher along exposed headlands and over the Wicklow Mountains. Up to 2” of rain can be expected over higher terrain from Ophelia. 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.
According to storm surge expert Hal Needham, extra-tropical cyclones sometimes cause substantial storm surges in high latitudes. For example, Pacific typhoons have become extra-tropical and generated storm surges of 12 feet in Western Alaska. Although Ophelia will maintain hurricane-force wind speeds close to the coast of Ireland, the storm will be moving with a forward speed near 30 mph on Monday. Such fast movement will reduce the ability of Ophelia to generate widespread storm surge. However, we still may see surge impacts where strong onshore winds blow into inlets or bays.
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.
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.
As we discussed in yesterday’s post, 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 winds 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 2. Visible satellite image of 92L as seen on Friday, October 13, 2017. GOES-16 data is considered preliminary and non-operational. Image credit: NOAA/RAMMB.
92L was under high wind shear of 20 - 25 knots on Friday morning, but had ocean temperatures warm enough for development: 28°C (82°F). Relative humidity at mid-levels of the atmosphere as analyzed by the 12Z Friday run of the SHIPS model was favorable for development, about 65%. Satellite loops showed that 92L had a modest area of heavy thunderstorms that were poorly organized, though a surface circulation was attempting to form just west of the area of heaviest thunderstorms.
The 0Z Friday runs of our top three models for predicting tropical cyclone genesis--the European, UKMET and GFS model--had two of them, the UKMET and European models, forecasting that 92L might develop into a tropical depression by Tuesday. Approximately 25% of the 70 members of the 0Z GFS and European model ensemble forecast showed development of 92L. The 12Z Friday run of the SHIPS model predicted that wind shear would remain high, 20 – 30 knots, over the next five days, which should keep development slow, and limit the potential for 92L to become anything more than a weak tropical storm. In their 2 pm Friday Tropical Weather Outlook, NHC gave 92L 2-day and 5-day odds of development of 10% and 30%, respectively. The most likely time frame for 92L’s closest approach to Bermuda will be Monday evening through Tuesday morning.