In a very rare occurrence, a former hurricane may hit Los Angeles this weekend with tropical storm-force winds (39-73 mph) and heavy rain. What is now Tropical Storm Hilary off the coast of Mainland Mexico is forecast to become a hurricane by 1 p.m. tomorrow and a major hurricane (Cat 3 and above) by 1 a.m. Saturday. By 1 p.m. Sunday Hilary is expected to become a lesser hurricane and then hit Southern California and potentially Los Angeles as a tropical storm. See National Weather Service forecast chart below.
Only two full-blown tropical storms have hit the coast of California in recorded history: the Long Beach tropical storm that made landfall near San Pedro in 1939 and and Hurricane Nora in 1997 after it was downgraded to a tropical storm. No tropical cyclone has ever made landfall in California at hurricane intensity in recorded history.
Two factors tend to keep Southern California safe from such storms: Colder sea surface temperatures, which take their fuel away, and upper level steering winds in the eastern Pacific. This year’s El Niño event means ocean temperatures are much warmer than usual, with the water in Malibu registering 70 degrees today. Normally, 67 or 68 degrees is the warmest coastal ocean temperatures get in the summer in Los Angeles.
Still, hurricane tracks are tricky to predict, especially four days out. The most recent National Weather Service forecast for Hilary indicates, “There remains a very large spread in the ultimate track so this remains a very low confidence forecast in terms of the track as well as the impacts. However, having said that, virtually all the GEFS ensemble members show moderate to heavy rain amounts, especially south of Pt. Conception.”
That rainfall is currently pegged at a very large accumulation for summer in Southern California with, per the NWS, “several solutions at or above 2.5″ and as high as 2.9″. So the probability of a very anomalous rain event is certainly increasing. The official rain total forecast currently is around 1-2″ area wide Sunday through Tuesday but with the potential for much higher (or lower) amounts depending on the actual track.”
There could also be lightning which, if it arrives with wind but without rain, could create fire danger.
In terms of waves, the NWS indicates Hilary “will bring the potential for hazardous marine conditions to all coastal waters starting this Sunday. While any wind/weather impacts from these systems over the local area are highly uncertain, long- period, steep, southerly swells and high surf will be possible during the upcoming weekend and beyond.”
Surf forecaster Surfline is currently predicting waves from 4-5′ feet’ in Northern L.A. County and 6-8′ in Northern Orange County. Those estimates can drop radically in 24 hours, however, should the storm hew closer to the coast of Baja California or rise considerably if it were to move out further into Southern California’s swell window. Indeed, just yesterday Surfline was predicting 15-20′ surf in Northern L.A., which would be a very rare occurrence for the region in summer.
Here is today’s NWS Los Angeles forecast:
Tropical storm Hilary is official now and expected to continue strengthening over the next couple days. The official track has it moving northwest, roughly parallel to the coast of Mexico, then west of the southern tip Baja Saturday morning. There remains a very large spread in the ultimate track so this remains a very low confidence forecast in terms of the track as well as the impacts. However, having said that, virtually all the GEFS ensemble members show moderate to heavy rain amounts, especially south of Pt Conception. The EPS is not far behind that now as the last few solutions have trended more towards the more northerly GEFS. The mean PW from both ensemble systems is now right at 2″ with several solutions at or above 2.5″ and as high as 2.9″. So the probability of a very anomalous rain event is certainly increasing. The official rain total forecast currently is around 1-2″ area-wide Sunday through Tuesday but with the potential for much higher (or lower) amounts depending on the actual track. The potential exists for isolated flooding and residents, particularly near burn scars should monitor the situation closely. The most likely period for the heaviest rain is later Sunday into Monday, though again the speed and track of the storm will impact the timing and rain intensity.
With the current forecast track there is also the potential for some gusty winds at times. Earlier models indicated as much as 8-9mb offshore LAX DAG gradient Sunday and Sunday night ahead of the storm arrival though more recent runs have backed off that slightly. There is still the potential for a “wet” Santa Ana wind event Sunday with gusty northeast winds in the usual areas across LA/Ventura Counties but it will probably take a couple more days to have much confidence in that forecast. Another potential impact will be the increase in south to southeast swells this weekend which could be high enough to create significant issues at south-facing harbors like Avalon and Long Beach, and even as far north as Morro Bay and Port San Luis along the Central Coast.
The storm is currently expected to exit the area by Tuesday but lingering southeast flow aloft will keep at least a chance of showers going through the end of next week.
