(KRON) — The first of at least seven straight days of rain begins Friday in the Bay Area as an atmospheric river is set to soak the region with a stream of subtropical moisture from Hawaii. The phenomenon, known as a Pineapple Express, generally brings heavy rain and mountain snow to the West Coa st. Is ‘Die Hard’ a Christmas movie? — vote in our poll “Prevailing winds cross over warm bands of tropical water vapor to form this ‘river,’ which travels across the Pacific as part of the global conveyor belt,” the NWS website reads. “When it reaches the west coast, the Pineapple Express can dump as much as 5 inches of rain on California in one day.” Friday marks the first of what could be three different rounds of rain coming to the region. The stormy weather is expected to increase in intensity by Saturday, bringing 30 mph winds and potential flooding. “Saturday will likely be the day where things begin to transition from beneficial to impactful,” the NWS forecast reads. “Through Saturday, the North Bay is expected to receive the brunt of the rainfall.” A Pineapple Express lines up with the Bay Area Thursday as the Bay Area is forecast for seven-straight-days of rain. (NASA Worldview) The second round of rain moves into the Bay Area Sunday. The strength of Sunday’s storm is unclear at this time, but rain is predicted for the region. “Moderate to heavy rainfall is expected across most of the region on Sunday,” the NWS forecast reads. “ Video: Driver passes CHP officer at more than 100 mph, gets pulled over Wind gusts up to 45 mph are possible Sunday. The combination of wind and heavy rain will increase chances for downed trees, potentially causing power outages across the Bay Area. “Additionally, any leaves that are left on trees will pose the risk of clogging storm drains when they fall, potentially leading to more flooding,” the NWS said. A Pineapple Express (left) takes shape over the Pacific on Dec. 17 (left) and Dec. 18 (right). (NASA Worldview) The third round of wind and rain arrives Tuesday and will continue into Christmas Eve. The stormy weather is expected to continue on Christmas Day. KRON4 will continue to monitor the latest Bay Area weather forecasts. “There is certainty that it is going to rain for the next seven days and likely into the Christmas holiday and beyond,” the NWS said. “Impacts will not only be felt with each individual system, but also the cumulative effect of the ones before it. All preparations for rain and wind should be done today. If you are travelling, please account for the weather and plan accordingly.” ...read more read less