This build is basically used for saving and ensuring kills for your team, and warding and using clarevoyance to know what the enemy team is up to.

Each of your abilities are useful in it's own way, Howling Gale knockups enemies so your team can nuke them down or escape when being chased, and as the knockup itself doesn't get better when leveling this ability up, i take it at level 2 and then wait until level 14. Zephyr pretty much has the same effect as Howling Gale, ensuring kills or saving your teammates, so i pick it at level 4 and whenever you cant level up your Eye of the Storm ability, as you get more movement speed from it and the enemies are slowed more. Eye of the Storm gives lots of attack damage, which allows your AD carry to nuke enemies undisturbed as well as it can save your teammates from spells like Ignite, so i take it at level 1 and max it asap, which means it gets t level 5 when you are level 9.
Monsoon, your Ultimate, is very useful when escaping or when you want to push enemies into your team, or just heal your whole team in teamfights, and it is awesome to use the Flash + Monsoon combo to get your enemies where you want them.

The masteries i have chosen are good for Health and Mana regeneration so that you can stay in your lane without having to recall all the time. These masteries is just how i want them and i'm sure there are other ways to spend your points so they fit your playing style more.

Your items are typical support items, giving you Health and Mana regeneration, gold over time and have effects that can help your team. Your Aegis of the legion and Soul Shroud grants useful auras to your team, Shurelya's Reverie can be used when your team needs to push, flee or just go somewhere quickly, and Rylai's Crystal Scepter slows your enemies so your teammates can chase them or flee, aswell as you get a little ability power which can be good when using Eye of the Storm or Monsoon to save someone. These items also gives some defensice bonuses so you wont be so squishy and you can survive to keep supporting your team.