She warned that the heavy rain could cause streams and rivers to rise rapidly. Driving conditions could become hazardous and motorists should watch for surface flooding and slips.
There was no wind warning in place but Crabtree said the region should also expect to see quite strong gusts.
"The rain will be starting on Monday night and then the wind on Tuesday will drive the second burst of rain."
This onflow would see the rain spread more evenly about the region with Central Hawke's Bay getting plenty, she said.
The heavy rainfall warning ends at 11pm on Tuesday, with the rain "clearing away gradually" on Wednesday and a few showers easing on Thursday.
Crabtree said the weather would brighten later in the week, with a "lovely" outlook for Friday and the weekend.
The rain will be come as a relief to many farmers across the region nervous about increasingly dry conditions - the Napier Airport gauge hasn't had a single millimetre of rain in the last 30 days.
Federated Farmers Hawke's Bay president Jim Galloway said it was positive news.
January saw Galloway record 15mm of rain on his Maraekakaho farm but he said it had been "patchy", and he hadn't had any rain so far this month.
"Some places got it but others five kilometres down the road didn't."
He said the heavy rain, even if mostly about the ranges, would be welcome as many farmers across the region were dependent on good water flows for irrigation takes.
The heavy rain late last year had seen strong grass growth over the last few weeks, allowing farmers to top up their supplementary feed, he said.
"The November rain really saved us.
"This time last year we had a lot less feed. This year we are in a far better position because it's later."
But there was still some concern among the farming community and it would be important for the rain to be followed up, he said.
Galloway said it was also important that farmers remained vigilant while dry conditions continued and a total fire ban remained in place for the region.
He also encouraged farmers to carry around fire extinguishers in farm vehicles and have water trailers ready to go.