Dr. Jeff Masters ·

Above: MODIS satellite image of Ophelia on Sunday morning, October 15, 2017. At the time, Ophelia was a Category 1 storm with 90 mph winds. Image credit: NASA.

Hurricane Ophelia was a weakening Category 1 hurricane with 90 mph winds late Sunday morning, as it sped north-northeast at 38 mph towards Ireland. Overnight, Ophelia skirted the Azores Islands, causing little trouble, but is likely to be a rare and damaging storm on Monday in Ireland.

Ophelia looked less impressive on satellite imagery o n Sunday afternoon, with an eye no longer visible, and the storm embedded in a front associated with a non-tropical low-pressure system to the north. Conditions for maintaining its tropical nature were growing very hostile, with sea surface temperatures (SSTs) a very chilly 21°C (70°F), and wind shear 35 knots and rising. Microwave satellite imagery showed that the inner core of Ophelia had collapsed Sunday morning, which will result in a weakening of the strongest winds.

Figure 1. Tracks of all tropical cyclones since 1851 to go east of 18 degrees west longitude. Ophelia is in rare company. Ophelia became a major hurricane on Saturday morning 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. Image credit: NOAA.

Ophelia had little impact on the Azores

Overnight, Ophelia brushed the Azores Islands, passing about 70 miles southeast of Santa Maria, the southeastern-most island of the Azores. Since the islands were on the weaker left-hand side of Ophelia, maximum sustained winds remained below tropical storm-force. Winds gusted as high as 44 mph at the Ponta Delgada airport on Saturday night, and a personal weather station in Ponta Delgada recorded 1.18” of rain from Ophelia. 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 2. Wind forecast from the 6Z Sunday run of the GFS model, valid at 12 UTC Monday, October 16, 2017. Sustained hurricane-force winds (120 kph or 74 mph, purple colors) were predicted in a small region along the southwest coast of Ireland, while tropical-storm-force winds (65 kph or 40 mph, light green colors) were predicted along much of the southern and western coast. Image credit: tropicaltidbits.com.

Ophelia will be a major damaging storm for Ireland

Ophelia is expected to complete the transition to an extratropical storm southwest of Ireland late Sunday night and early Monday morning. As this process unfolds, the wind field will expand, and top winds will weaken to about 120 kph (74 mph), but Ophelia still promises to be a large-scale damaging wind event for Ireland. The Irish weather service has issued a Red Alert for western Ireland for Monday, including Galway, Mayo, Clare, Cork and Kerry Counties, where sustained winds over 80 kph (50 mph) and gusts over 130 kph (80 mph) are expected. Expect tree damage and uprooted trees, damaged roofs, power blackouts, mobile phone coverage interruptions, and flying debris. An orange wind warning has been issued for the remainder of Ireland, where maximum sustained winds of 65 – 80 kph (40 – 50 mph) are likely, with gusts up to 110 – 130 kph (70 – 80 mph.) The U.K. Met Office has issued an amber warning for wind on Monday in Northern Ireland. The warning indicates that some transportation delays are possible, and there is a chance of power outages.

Winds will begin to strengthen in southern Ireland in the pre-dawn hours Monday morning, with tropical storm-force winds arriving near dawn. The main impact will come Monday afternoon and evening, though. The center of Ophelia will reach the southwest coast of Ireland near noon local time, and will take about six hours to cross the island. An intense 3 to 6-hour period of high winds and rains of 25 – 75 mm (1 - 3”) will accompany the storm. In higher terrain, winds will be about 30% higher than at sea level, and an extra 25 mm (1”) of rain can be expected.

Sunset visible image from Meteosat SEVIRI of #Ophelia as a major hurricane. Another stunning storm in 2017's ridiculous season. pic.twitter.com/QlXnGjFHSQ — Simon Lee (@SimonLeeWx) October 14, 2017

Storm surge

Although Ophelia will maintain hurricane-force wind speeds to the coast of Ireland, the storm will be moving with a forward speed near 40 mph on Monday. Such fast movement will reduce the ability of Ophelia to generate widespread storm surge. However, Ophelia will be capable of generating a storm surge of 2 – 4 feet, which may cause coastal flooding where strong onshore winds blow into inlets or bays. Tidal range is about 8 feet, so it matters greatly if the peak storm surge arrives at high tide or low tide. It currently appears that the highest storm surge will arrive at the southern coast of Ireland near noon local time, about two hours after low tide (approximately 10 am local time). High tide is near 4 pm local time on Monday, and the highest storm surge flooding will likely occur during the early afternoon as the tide comes in, after the center of Ophelia has passed the south coast of Ireland.

The only comparable storm to hit Ireland: Hurricane Debbie (1961)

The only comparable storm to hit Ireland is Hurricane Debbie of 1961, which brushed the west coast of Ireland on September 16 as a Category 1 hurricane, producing major destruction. Wind gusts reached 171 kph (106 mph) at Ballykelly and 168 kph (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. Our Saturday post has a full accounting of the history of ex-hurricanes that have hit Ireland and Britain.

Figure 3. Visible satellite image of 92L as seen at 1 pm EDT Sunday, October 15, 2017. A closed center of circulation was attempting to form about 100 miles north of the eastern tip of the Dominican Republic. Image credit: NOAA/RAMMB. GOES-16 imagery is considered preliminary and non-operational.

92L north of the Dominican Republic may affect Bermuda on Tuesday

A broad area of low pressure was located about 150 miles north of the eastern tip of the Dominican Republic on Sunday afternoon, and was headed west-northwest at about 15 mph. This system (92L) was bringing heavy rain showers to the Leeward Islands, Virgin Islands, and Puerto Rico, as seen on Martinique radar. This system has the potential to develop into a tropical depression by Tuesday as it moves northwest and then northwards towards Bermuda. No other land areas are likely to be impacted by 92L.

92L was under high wind shear near 35 knots on Sunday afternoon, but had ocean temperatures warm enough for development: 29°C (84°F). Relative humidity at mid-levels of the atmosphere as analyzed by the 12Z Sunday 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, with a surface circulation attempting to form several hundred miles to the west of the heaviest thunderstorms.

Forecast for 92L

The 0Z Sunday runs of our top three models for predicting tropical cyclone genesis--the European, UKMET and GFS model--had two of them, the UKMET and GFS models, predict some weak development of 92L by Tuesday. Approximately 20% of the 70 members of the 0Z Sunday GFS and European model ensemble forecasts showed development of 92L into a tropical depression. The 12Z Sunday run of the SHIPS model predicted that wind shear would diminish to 15 - 25 knots on Monday and Tuesday, which may allow 92L to organize into a tropical depression by Tuesday. Wind shear was then predicted to rise above 40 knots by Wednesday as 92L merged with a cold front, which would discourage further development. In their 2 pm Sunday Tropical Weather Outlook, NHC gave 92L 2-day and 5-day odds of development of 30% and 50%, respectively. The most likely time frame for 92L’s closest approach to Bermuda is Tuesday morning.