Ever spent a large portion of the day at the beach watching the red and yellow flags changing direction pondering what was going on with the winds? Tomorrow will be a good day to notice the effects the sea breeze has across the Sydney basin and how it shapes people's life from the eastern suburbs, through the inner west and the western suburbs. Today and tomorrow, we will be looking at what sea breezes are, how they form and its effects in Sydney, although the principle can be applied to the eastern seaboard in general. Sea breezes form by the difference in temperature over the ocean and the adjacent land area. On a hot, sunny day (mainly spring and summer) the air above the ocean will warm very slowly, with the ocean absorbing most of the heat. On the other hand, the air above land will warm up much quicker. During spring, sea surface temperatures are very cold having just come out of the colder winter months. Further inland, increased sunshine during spring allows the warming effect of the land to reach its maximum. Hence, the contrast between the cooler sea surface temperatures and the land becomes significant during the day, peaking at about mid-afternoon. Going back to science 101, we know that warm air rises (over the land) while cool air sinks (over the ocean). To replace the air going up over land, the cool surface air over the ocean is brought in over the land. As it penetrates further inland it warms and ascends. The ascending air over the land then returns seawards (at about 100 to 1000m above the surface), gradually cooling down and eventually sinking down to the surface of the ocean. This provides a continuous circulation of the air. On an average day, the sea breeze will commence along the coastal fringe as soon as the temperature over land exceeds that of the adjacent ocean. As the temperature over land increases during the day so does the difference in temperature between land and ocean, leading to a stronger sea breeze. The stronger the sea breeze the further inland it will go. A typical late spring/early summer sea breeze may extend 80 to 160km inland during the afternoon. Even Canberra, which is about 120km inland and 600 m above sea level does experience summer sea breezes. Sea breezes of about 15-20knots will occur after a couple of hours of attaining the maximum temperature, typically at about mid-to-late afternoon. Along the eastern seaboard, sea breezes will initially form at right angles to the shoreline. But as the day progresses and the sea breeze become stronger these tend to back anti-clockwise due to the Coriolis Effect. A sea breeze in Sydney will have a northeast direction by mid-afternoon. A weak sea breeze will likely die just after the sunset, but a stronger sea breeze can last until closer to midnight.