The high has continued to track northeast, and is currently centered over southern Sweden. Nevertheless, this feature will remain the driving force for the winds through the weekend. As a result the SE'ly pressure gradient around the back side of the high will drive a weak offshore flow in the course area, likely oscillating between E'ly and S'ly.
Thus the real question for the in-port race today, is how quickly will the SE'ly flow decrease and how much (if any) will the thermal gradient develop? As usual the fewer the clouds and the more sun there is the more of a thermal gradient you can expect.
In addition, the weaker the offshore flow in the morning, the earlier you can expect the breeze to fill for the afternoon. While a weak offshore gradient can sometimes help develop an afternoon sea breeze, a stronger offshore gradient may be too much for the sea breeze to overpower. As a result, the early wind speed is likely to play a big role in the conditions today. The sooner the offshore gradient decreases the more likely you are to see a building afternoon sea breeze. On the other hand, if the offshore winds remain strong, the thermal gradient may not build enough to drive any afternoon build.
FORECAST DISCUSSION: The strongest winds of the day are expected to be in the early morning, likely decreasing and shifting right through the day. By noon the winds are likely to drop to below 10 knots. The more the winds decrease through the late morning the more likely you are to see the sea breeze fill for the end of the day.
On the outer Bay this may mean the winds back to a SW'ly flow; however the inner Bay may only see decreasing wind speeds as the thermal gradient fights the existing pressure gradient. If the winds stay around 10 knots through the early afternoon, look for a continued decreasing trend, with the wind speeds not likely to build again until after sunset.
WEATHER: Bright and sunny, with some clouds lingering offshore, and some possible cumulus development. Temperatures will increase through the day, with a high near 18 C (65F). The offshore flow will make it feel warmer, but watch for a cooler afternoon if the breeze fills out of the S or SW.
Detailed Wind Forecast for the inner part of Galway Bay (30 MAY 2009):
Time Wind Speed Wind Direction
(LT) Mean Range Mean Range
0900 12 10-15 165 140-180
1000 12 10-15 160 150-190 ...shifty/puffy with offshore flow
1100 11 09-14 170 150-190 ...decreasing winds
1200 10 08-13 170 150-190
1300 09 07-12 175 150-190 ...more decrease/offshore, more backing
1400 08 06-11 175 150-190 ...sea breeze offshore, light in Bay.
1500 06 04-09 180 150-190 ...may become light and variable
1600 07 04-09 170 140-180
1700 08 05-10 165 140-180
1800 09 06-11 160 140-180 ...building again as SSE for evening
HEDGE: Forecast Confidence: BELOW AVERAGE.
1. There is reasonable model agreement for a decreasing offshore pressure gradient, and marginal agreement between the early observations and model guidance. Thus, the big question for today is whether the sea breeze will fill for the afternoon or just fight the existing gradient.
2. Look for the strongest winds of the day to be in the early morning. Currently the observations are showing a NE'ly flow with speeds near 8 knots. The breeze is expected to veer right and build out of the SE when the sun comes up and the stronger flow mixes down to the surface.
3. The stronger the midmorning winds the more SE'ly they will be and the longer they will last. Look for gusty conditions with stronger SE'ly gusts mixing down through noon.
4. For the afternoon the wind speeds are expected to decrease, likely veering right to S'ly. With light enough winds the outer part of the bay may see a weak sea breeze fill out of the SW. This SW'ly breeze is not likely to make it into the course area. In fact the more the SW'ly flow builds on the outer part of Galway Bay, the more of a convergence zone that will develop in the sailing area and the lighter the winds will be.
5. If the winds speeds are less than 5 knots look for large oscillations in direction.
6. The more the thermal develops, the more the convergence zone will move into the sailing area. In this case look for any puffy cumulus clouds to be an indication of a convergence zone. The winds under the clouds (in the convergence zone) will be very light, with lighter SE'ly winds inside the line of clouds and stronger SW'ly flow outside the line of clouds.
7. If the early winds are much lighter than expected and the sea breeze does fill, look for early SW'ly flow to shift to W or even WNW. This is unlikely, but you could see winds fill to 10+ knots, with cumulus clouds developing over Ireland.
OUTLOOK FOR THE NEXT FEW DAYS:
Sunday: Look for increasing clouds as a complicated, but stalled frontal boundary sits to the west of Galway. Meanwhile a weak ridge of high pressure will extend southwest from the large high, driving light winds. The winds will stay out of the ESE to ENE, likely dropping to less than 10 knots for the whole day. The lightest winds of the day are expected to be midday. With clear skies, a sea breeze may develop, and you could have better velocity in the afternoon.
Monday: The ridge will continue to dominate the conditions with a generally weak pressure gradient driving light winds in the course area. Meanwhile, the upper level trough will continue to deepen to the west of Galway, but it will have little influence over the conditions on course. As a result, the winds on course will be light, struggling to reach 10 knots. Clear skies and light morning winds mean you will need to watch for a developing afternoon thermal. In this case the sea breeze would drive SW'ly winds to around 10 knots.
Extended: The large upper level trough is still expected to dig south, eventually breaking off to the west of the course area; however this will not influence the conditions on course until late next week. Otherwise look for continued light winds and warm temperatures. The end of next week will see a cooling trend with some rain likely.
