There is no official word on the Forgotten Realms lesser deity Shaundakul in 5e. He has not been mentioned in Realms materials since 3e, but has never been confirmed as dead.
As far as Shaundakul in 5e, the closest to an official word is probably Realms author Erik Scott de Bie's long-running (nearly 3 years now) two-part thread, "One Canon, One Story, One Realms (5e)," on the Candlekeep forums seeking "to create an all-inclusive vision of the setting that is open to all eras, and even all editions of the game." Shaundakul is mentioned at several points, but there has been no confirmation as of yet that he will be included in 5e published Realms material.
If your 5e campaign is set in the Forgotten Realms, Umberlee, goddess of the sea, would probably be your best bet and is listed in the Player's Handbook on page 294. Historically, she is a chaotic evil intermediate power (i.e., one step above Shaundakul in godly ranking). Her portfolio in 3e was oceans, currents, waves, and sea
winds. Since there is nothing more than a list of deities in 5e right now, you may want to look to earlier editions for more thorough descriptions of Umberlee. For example, the 4e Forgotten Realms Campaign Guide describes her as:
The Queen of the Deeps is a harsh mistress, largely uncaring of her mortal worshipers' pleas for mercy when one of her storms whips the seas of Toril into a killing frenzy. Still, hardly a soul steps aboard a ship who doesn't whisper at least a cursory appeal to her in the hope that her random mercies fall their way.
Her waveservants rely on the scattered alms of terrified sailors for a minimal living, preaching the majesty of the uncaring ocean and the inherent hopelessness of anyone who dares set to sea. (FRCG, p. 78)
She can also be found on page 254 of the 3e Forgotten Realms Campaign Setting and page 173 of 2e's Faiths & Avatars.
As OP noted, Selûne is another excellent choice found in the 5e PHB. In 3e, she was an intermediate power whose portfolio included the moon, stars, navigation, navigators, wanderers, questers, and good and neutral lycanthropes. Then, she transitioned to a greater goddess in 4e and is listed as goddess of the moon in the 5e PHB. For more information on Selûne from previous editions see page 76 of the FRCG (4e), pages 248-249 in the FRCS (3e) and F&A (2e), pages 133-138.