** Neptune Insurance's NP.N shares jump 12.5% above their initial public offering price in NYSE debut
** Stock opens for trading at $22.50 vs IPO price of $20 apiece; shares last up 15.4% at $23.08 in afternoon trading
** Flood insurer and some of its existing shareholders on Tuesday sold 18.4 million shares to raise $368 million in its IPO
** Neptune's listing is the sixth insurance IPO in New York since May, according to data compiled by LSEG
** Founded in 2018, Neptune's business is heavily concentrated in Florida — a market where some large national insurers have scaled back their presence in recent years due to frequent natural disasters
** Morgan Stanley, J.P. Morgan and BofA Securities were the joint book-running managers for the offering
(Reporting by Anuj T in Bengaluru)
((anuj.t@thomsonreuters.com))