Sweet, but little insignificant question. Wouldn't the Hidden Mist technique sorta count as the first weather manipulation jutsu? Lol, it doesn't matter though
Itachi performs the six hand seals and then begins to release his chakra. A cloud begins to form above him that is about 20 meters wide. Itachi then continues to expel his chakra in the form of the rain which cause drops of water to pour down. Closing his eyes in an attempt to purely sense, he then allows the water to fall, and then notices the presence of his sensei being hit by the water.
(Suiton: Ukojizai no Jutsu) - Water Style: Rain Tiger at Will Technique
This technique is useful given that it's primary purpose is sensing, and this allows for long range sensing. Effectively, the user can find the location of a person as it would be impossible to avoid the rain drops. This means a user can continuously track a target as well. An issue though is that the technique does not allow for clear and precise sensing, merely rough rudimentary ones. That being said, I'd assume that a downside would be that if a target has his chakra spread out in several areas, the user of the technique would not even be able to really sense the target. If I were to counter, I'd probably use the hidden mist technique, as the mist uses chakra to stay active and to affect it's thickness. This would spread my chakra around the same range of the rain, which since the rain would hit everywhere the mist is, the user of the technique would have trouble locating me, if at all.
Itachi performs the six hand seals and then begins to release his chakra. A cloud begins to form above him that is about 20 meters wide. Itachi then continues to expel his chakra in the form of the rain which cause drops of water to pour down. Closing his eyes in an attempt to purely sense, he then allows the water to fall, and then notices the presence of his sensei being hit by the water.
(Suiton: Ukojizai no Jutsu) - Water Style: Rain Tiger at Will Technique
Rank: C
Type: Supplementary
Range: Short-Long
Chakra cost: 15
Damage Points: N/A
Description: A perception ninjutsu, allowing one to freely manipulate rain infused with the user's own chakra after waving the Bird → Rat → Ox → Monkey → Rat → Snake hand seals. The rain falls from rain clouds, formed with the users own chakra. During this technique, the falling raindrops are closely linked to the users senses. When the rain is obstructed by a chakra belonging to someone the existence of the target can be detected. The rain will keep on falling until the user uses the seal to cancel it.
Type: Supplementary
Range: Short-Long
Chakra cost: 15
Damage Points: N/A
Description: A perception ninjutsu, allowing one to freely manipulate rain infused with the user's own chakra after waving the Bird → Rat → Ox → Monkey → Rat → Snake hand seals. The rain falls from rain clouds, formed with the users own chakra. During this technique, the falling raindrops are closely linked to the users senses. When the rain is obstructed by a chakra belonging to someone the existence of the target can be detected. The rain will keep on falling until the user uses the seal to cancel it.