The following are idiomatic in American English: What a brave soldier he is! What a brave soldier is he! (poetic, literary) How brave a soldier he is! How heavy the rain is! -> Also: How heavy the rain is today! How brave a soldier is he! (poetic, literary) How beautiful the flowers are! EDIT to add: And you would not usually use 'a' with 'weather'. ------------------------------------------------------------------------------------------------------------------------------------- EDIT 2: The basic rule here is Use 'What" when a noun phrase (NP) follows: What a brave soldier he is!. The NP is 'a brave soldier'. Use 'How' when an adjective or adjectival phrase follows: How beautiful the flowers are! The ADJ is 'beautiful'. How economical this car is! How troubling these times are! How incredibly delicious-tasting this cake is! 'incredibly delicious-tasting' is an adjectival phrase: He bought the incredibly delicious-tasting cake at the supermarket. Because this adjectival phrase is kind of long, it would be common to reverse the order of the predicate: 'How incredibly delicious-tasting is this cake! How great thou art! ADJ is 'great' You also use 'How' when an adverb or adverbial phrase follows: How wonderfully he sang the song! The ADV is 'wonderfully'. How hard the rain is falling! The ADV here is 'hard'. It is called a flat adverb, because it does not end in -ly.

There are many ways we may phrase exclamations. Here are my answers to your questions: 1. How + adj+a(the) noun.+be . : NOT native : e.g. How heavy the rain is /how bad the weather is/ (NOT native ) - Normally we would say: LOOK how heavy that rain is! LOOK how bad the weather is (or has become)! 2 .What+ (a)+adj.+noun.: native . eg . What a heavy rain ( it is) / What a bad weather(it is) (native ) - We would normally say: What (a) heavy rain! What lousy weather! 3.Please confirm it is native if I use " how + adj.+ it is " (e.g. how beautiful it is ) ( I would not say " How beautiful the flowers are ! right ? ) - I could say any of these: How beautiful that is! How beautiful those flowers are! Look how beautiful those flowers are! (Weather is an uncountable noun, so you cannot say "a weather", which would mean "one weather".)