Storm Desmond - High Winds 4/5 December 2015

My take on the latest guidance is that it continues the themes already developed in this thread.

On the wind potential, that will be mostly a west coast issue and because the wind direction is SSW to SW, the direct impact on Galway Bay will be less able to transfer strong winds inland there, than with similar westerly gale to storm force wind events. When the stronger winds spread further east by Saturday morning, they will only be level one in a few locations, but it should be stressed that level two wind alert conditions will be almost steady state from mid-day Friday to late Saturday on the Atlantic coasts especially around Belmullet. Peak gusts in the 120 to 130 km/hr range appear likely there.

As to the rain potential, this will actually exceed level two in a few parts of the west, notably Connemara and western Mayo, Donegal, some parts of Clare and higher terrain in Kerry and nearby west Cork and Limerick, so a level three rain advisory should be in place locally where streams flow out of higher ground in those counties, especially Connemara from the guidance -- level two somewhat more widespread in the western coastal regions, and level one extending a few more kms inland and here or there in higher parts of the central and southern, eastern counties. It probably won't reach advisory levels in some places in lower elevations of the central and eastern counties but more depends on where rivers rise and drain, than what rainfall they receive locally, so would factor that into any planning considerations.

To summarize then, this will be a significant wind event mainly in west coastal locations and a significant rainfall event mainly on or near high terrain. Fortunately the heavy rain potential does not overlap the areas flooded today in the southeast except possibly over some parts of Wicklow and Carlow near the higher portions of the Wicklow Mountains. That area should be watched for renewed flood potential.

It will be interesting to hear from Galway posters about how water flows develop into the city from nearby lakes as I gather those watersheds are partially managed flows, and having lakes involved can slow down the rate of flooding downstream, however, it may become an actionable situation independent of how much rain falls on the city since the problem is mainly created upstream. I would expect perhaps 35 to 50 mm of rain in Galway city (compared to 100-150 in nearby Connemara) over the period Friday to Sunday. As Oneiric3 suggests, many areas of Connacht should take a moderate rainfall advisory seriously as water levels are already quite high. Flooding may be difficult to avoid if many rivers are already near bankfull levels.

The guidance suggests that total rainfalls of 50-100 mm are likely over these higher areas and locally could reach 150 mm. Then there will be further similar amounts from Monday to Thursday in several more rounds. Some lower portions of central counties may only see 10-20 mm in these same intervals, so it will be mostly a localized (although severe in potential) rain-flood event.