1. Expression of Time
In this web site, we use two types of expressions for time.
UTC (Universal Time Coordinates)
In the field of meteorology, UTC is practically equivalent to Greenwich Meridian Time (GMT), but the exact definition of UTC and GMT is different. The notation of 'Z' means 0 hour difference from GMT (UTC) originally came from marine navigation, and it is pronounced as 'Zulu time' because 'Z' is 'Zulu' in the phonetic alphabet.
JST (Japan Standard Time)
Japan Standard Time, which is nine hours advanced to UTC. It is sometimes described as (+09) in the last part of the time.
Most of the expression of time in this web site is based on UTC, because that is the standard time used in international meteorological observations. When the time is based on JST, it is so written explicitly.
For example, 00 UTC = 09 JST, 12 UTC = 21 JST, 18 UTC = 03 JST (the next day). And the noon in Japan 12 JST = 03 UTC. Please check the expression of time when you refer to specific data.