As StoneyB suggested, roar and crash of the surf are common descriptions. Roar is used in sense 4, “Generally, of inanimate objects etc., to make a loud resounding noise”, and crash in sense 3, “A loud sound as made for example by cymbals”.
Some other terms often used include pounding surf, in sense “Causing heavy or loud throbs”, and rumble of surf, in sense “A low pitched irregular noise, such as that of thunder or a hungry stomach”.
Ngrams for pounding surf,rumbling surf,rumble of surf,roaring surf,roar of surf,crashing surf shows pounding surf coming first since about 1930, before which time roaring surf was most common among those phrases. In recent years, crashing surf has pushed roaring surf out of second place. (It is possible other forms and combinations not included in that ngrams, such as “roar of the surf” instead of “roar of surf”, may occur more frequently; feel free to try different phrases, time periods, smoothing, etc.)
From en.wiktionary, susurrus means “A whispering or rustling sound; a murmur”; although susurrus obviously doesn't apply to loud surf, google for susurrus of the surf shows that phrase appearing in several recent books.
If you're describing liquids that are too hot for you, use scalding:
very hot; burning.
e.g. Watch out, the tea is still scaldingly hot!
For food or liquids that are a pleasant temperature, use piping:
(of food or water) very hot.
e.g. "The food's piping hot!"
Best Answer
Your grandmother is shivering. The word you are using is called an onomatopoeia, which is a word that is spelled in such a way as to make the sound.
Different cultures around the world make sounds differently. See, for example, this Wikipedia page. Often, Americans will spell the sound "brr." In Russia, I saw it spelled "zhzh" (actually it was in Cyrillic, but this is the English equivalent).