just in case you're all curious..."Henry Hub is the pricing point for natural gas futures contracts traded in the New York Mercantile Exchange, or NYMEX. It is a point on the natural gas pipeline system in southern Louisiana. It is owned by Sabine Pipe Line LLC.

It interconnects with nine interstate and four intrastate pipelines: Acadian, Columbia Gulf, Gulf South Pipeline, Bridgeline, NGPL, Sea Robin, Southern, Texas Gas, Transco, Trunkline, Jefferson Island, and Sabine. The two compressor stations can compress 520,000 decatherm/d (6.3 GW) . The transportation capacity is 1.8 billion ft³/d (590 m³/s)."

What is the difference between

Nymex Henry Hub

Henry Hub

and New York City Gate?

And why do they differ so much?

NYMEX HB = $12.32 and Henry Hub is $2 more. NYC Gate is $15.

Could someone explain those numbers?

Not sure on your Henry Hub price vs Henry Hub NYMEX, maybe spot vs future (today vs next month) but NYC gate is the citygate price for gas physically in NYC vs Henry Hub in Lousiana. Transport fees and fuel usage would make NY MMBTU more expensive than HH MMBTU.