Wednesday, 2 October, 2019
Forecasts for Ireland
Update on Lorenzo -- Hurricane Lorenzo has recently moved past the western Azores islands of Flores and Corvo, with hurricane force gusts reported. It is already about 150 miles northeast of them now and moving very rapidly towards Ireland. The main portion of the Azores had some tropical storm force winds at times but escaped the main hurricane bands with some squally showers overnight. Almost all guidance now shows Lorenzo becoming "extra-tropical" (a more traditional low in other words) in the next 24 hours, then approaching Connacht in a gradually weakening condition, finally swerving southeast from Donegal Bay to make a landfall between Mayo and southwest Donegal by Thursday evening, and the steadily weakening low tracking southeast towards Dublin overnight, then crossing the south Irish Sea Friday morning.
Forecasts here are based on the prudent choice of a somewhat higher end of the range of possibilities as maps hint at a weakening trend developing just before the landfall stage. It should be noted that Lorenzo will be tracking fairly close to the coast for 9 to 12 hours before making the landfall so that weakening might not apply to its strength while approaching the coast. And a key point is that the elevated sea state conditions, with large swells and breaking waves likely out ahead of the storm, would not be much affected by any weakening trends late in the period. The ocean effects will be the most reliable part of the projected scenario and Galway Bay in particular as well as other west coast bays should be prepared for some coastal inundation and battering waves on exposed shores.
(Trends are the same as reported yesterday and will return once Lorenzo is past).
TODAY will see a gradual increase in cloud and the arrival of lower cloud layers in the west by afternoon, but the sun will be dimly visible through the higher cloud layers. It will feel rather brisk despite a drop in wind speeds for most of the day. Winds will be veering gradually around from northeast to southeast as a weak ridge drifts east, and the start of the southerly flow ahead of Lorenzo arrives tonight. Highs today will reach about 15 C in the south and 12 C in parts of the north.
TONIGHT will continue overcast with a slowly increasing southeast wind reaching 40-60 km/hr at times near south coast. Rain may move into some western areas towards morning. Lows will be 7 to 10 C.
THURSDAY will be cloudy with increasingly strong southeast to south winds, and intervals of rain. Rather mild with highs 17 to 20 C. Winds will be 50 to 80 km/hr for most areas during the day, but could reach 80-110 km/hr by late afternoon on the west coast. Rainfalls of 5-10 mm will be widespread, 15-20 mm in Donegal and perhaps northwest Mayo. Although the centre of Lorenzo will remain off the coast, large swells and waves will impact the west coast and to a lesser extent other coasts, by mid-day and through the afternoon.
THURSDAY NIGHT will see the strongest impacts on land, and as discussed, there is some chance that the storm will tend to blow itself out over the ocean just before hitting land. However, in the event that it retains some intensity to landfall, there is a risk of winds in the 80-120 km/hr range in coastal Connacht and 70-110 km/hr in west Munster, later extending into the midlands. These will veer from southwest to west then northwest as the low tracks into central Ireland. Some outbreaks of heavy rain (20-30 mm) are likely north of the track, with a few squally showers near and to the south of the track (a further 5-15 mm there). Temperatures will be steady 10 to 13 C. The southeast will likely remain less windy throughout and conditions from Dublin to Waterford and possibly as far as Cork could be relatively moderate until morning.
FRIDAY the remnants of Lorenzo will be tracking south of Dublin if not over the capital, but with much reduced wind speeds in general. Once into the Irish Sea, winds may pick up briefly from the north at 50-80 km/hr. Otherwise most parts of the country will soon be in a more moderate northwest wind flow, backing around to westerly. Some bands of rain or showers will persist for the morning hours then a gradual clearing is expected once the weak remnants of Lorenzo reach southern England. Highs will reach about 16 or 17 C.
SATURDAY will be mild with intervals of rain and southerly winds 50 to 80 km/hr, clearing by afternoon with winds easing to westerly 40 to 60 km/hr. Lows near 10 C and highs near 16 C. Temperatures will fall rapidly Saturday night.
SUNDAY will be partly cloudy and cooler with lows near 4 C and highs near 13 C. Another batch of wind and rain is expected by Sunday night into Monday.
The outlook for next week is for colder weather to arrive after the Monday frontal system moves through, highs with that around 15 C but later in the week closer to 10-12 C, and some risk of slight frosts at night.
My local weather on Tuesday was partly cloudy and still rather cold, highs near 10 C. The snow has pretty much disappeared in town now but still lies 15 to 30 cm thick over higher terrain close by to the northwest. We have had little leaf fall yet although a nearly complete change in autumn colours (the local forests however are mostly coniferous, only in the town and lower down into the Columbia valley can one find many autumn colours on display).
Watch for updates on Lorenzo.