he is in a cave but you have to get the guy at the weather institute to tell you where he is at
Beat the elite four first.
The weatherman is in Route 119. He is inside the weather institute west of the bridge in Route 119.
check the guy in the guy in the top floor of the weather institute near foretree city
go to the weather place after beating the game.one guy will say wierd weather patterns. one area is groundon one area is kyogre.
sea cavern but first you have to beat the elite 4 and talk to the guy in the weather institute
Sea LairHere is advice: Pokemon emerald on routes 105 127 129 103You find out where it is when you beat the elite four and go to the weather institute and talk to the guy who gives you castform after you catch groudon. The guy is located on the top floor.
The Castform that you get from the guy at the Weather Institute has a Mystic Water attached to it. When held by a Pokemon,the Mystic Water raises the power of its Water-Type moves.
You can get strength in Pokemon emerald by using rocksmash on the rocks in Verdanturf tunnel. a guy will give it to you
There is not a weather institute in Pokemon Heartgold, you are thinking of Pokemon ruby, sapphire, and emerald, there is not a weather institute in Pokemon heartgold.
In Pokemon Sapphire, you can capture Kyogre after encountering it once in the cave where you met Archie. Kyogre will flee to Sootopolis City and arrive in the Cave of Origin, north of Sootopolis City. You will need to trade for Kyogre from Pokemon Sapphire or Emerald to obtain it in Pokemon Ruby. In Pokemon Emerald, Kyogre can be found in Marine Cave when the guy at the Weather Institute announce bad weather in the sea.
you go to the weather institute and you talk to the guy who gave you the castform and he tells you its either raining on this route or sunny on that route hope i helped!