Daniel Swain Offices Hours 8/16/23
My rough notes from the last session, including a few of the jokes.
Topics: More thoughts on Maui wildfire disaster, then discussion of thunderstorm risk in CA this week and possibility that remnants of an East Pacific hurricane could affect CA in ~a week.
These are my very rough notes so treat them accordingly. Also like last time, I’m going to flag anything I may have gotten wrong with a (❓). This means I may have heard wrong, misunderstood, or was just my interpretation.
If you want to watch these yourself, skip ahead to about the 7-7.5 minute mark. He had to work through some streaming issues.
My rough notes
Brief additional thoughts on Maui, and the conversation about these events, then majority of session on California since weather activity increasing
Some pockets of significant thunderstorm activity, lightning started some fires, additional activity next ~48 hours
Potential for an intact but weakening tropical cyclone (hurricane Hilary) hitting California
On Maui:
Over 100 deaths, most deadly wildfire
Have been more fires on Maui recently, land management has contributed, climate change has contributed
In previous office hours/conversation, commented that tying climate change to this event is difficult, but not impossible
Some research on precip patterns and overall warming trend is likely to increase preconditions for dry side to be prone to fire
As a reminder, quoted from last office hours (quote too long/quick for me to add here), point was that wildfires are very complex events, you can’t just put it all in a single sound bite. These YouTube events are broader, unpolished, stream of consciousness.
Sounds like there was some misuse of his comments from previous office hours
Need to listen to the entire conversation, not just a few minutes of the session
Never a single cause for a disaster, usually a confluence of factors that contribute (climate change, land management, ecosystem, etc.), not any one of these is always the primary contributor, it depends on the situation
Lots going on in CA, going chronologically
Past couple of days, south east winds (winds coming from south east to north west broadly), has brought subtropical air, isolated to scattered showers
At least a dozen fires started
Some areas still benefiting from wet winter (higher elevations), but seems like fire season may have been kicked off in some areas (still not as severe as August 2022 (❓not sure i got the year right since he mentioned 2020 later))
Northern 3rd to 1/2 of California could see more fire activity over next ~48 hours
Big story though is hurricane Hilary (was tropical storm when the office hours were recorded)
Models pointing towards north-north west along Baja California, at least SoCal looking at significant impacts
Ocean temps along Baja are warmer than average, does provide extra hurricane fuel, north of this point waters are closer to normal temps
Important part though is that other weather patterns are going to allow this storm not to recurve away from the coast, cutoff low and high pressure systems working together to impact hurricane Hilary/tropical storm path
High pressure ridge is going to prevent normal wind patterns from recurving the storm, will get stuck on the far western side of the ridge and low pressure system to the west
Want to be clear, unlikely an intact tropical storm will actually make landfall in SoCal, but not impossible, been a long time since something like this made landfall (~1930s)
Some indications that rains and flooding could be worse than Kay (think Kay was last year ❓)
Potential for a year or more worth of precipitation in the deserts over very short time
Do not need landfall for these precip threats
Returning to storm center
Potential for actual landfall at or near tropical storm strength, may technically be classified as post-tropical storm but still
Different from typical winter storm
Not too often NWS offices in SD and LA coordinating with national hurricane center but likely happening with this system
Back in 97 hurricane Linda was similar to Hilary, could make landfall between SD and LA, Linda actually prompted first plans for tropical storm watches for CA (❓I think “tropical storm watch” was the right phrase)
Often think of these events as a novelty, but on Sunday and Monday the impacts could be significant
Impacts depend on trajectory of storm, will do a blog post and another office hours to cover specifics
Right now (on Wednesday), biggest concern is flash flooding on eastern CA slopes and desert areas, depending on system location could impact central and NorCal, could actually bring rainy days hopefully without lightning
Would bring easterly wind patterns though, NorCal could see benefits or it could see less rain and more lightning instead, wide range of impacts and have to see where storm goes
Why CA doesn’t see more tropical storms or hurricanes despite it’s relatively low latitude, for example, on east coast at same latitude you see high risk of hurricanes
Difference in water temps, west coast waters are cooler
Two other key reasons: level of atmospheric moisture is low in summer months, CA is in a region of downward air movement (❓)
One weakness that allows systems to sneak through, hurricane off Baja needs to be strong enough, then need other weather patterns to direct storm (❓)
Loophole is strong enough hurricane that doesn’t fall apart before it can make landfall
Hilary shouldn’t be a strong storm, should be falling apart, but not fast enough for it not to have impacts on CA
Woo, takes sip of water
Time for questions
How much could recent thunderstorms and historic heat impact fire season?
In PacNW and NorCal, we have some serious fires going now, areas of Northwest Territories in Canada getting evacuated
Northern 3rd of CA have recent ignitions
One silver lining, remnants of Hilary could help if we get mostly rain
Rainfall in LA from Hilary
Range of precip amounts from .25 to 5-6+ inches
Latter would be record breaking
Is there any good reason that changing climate could bring more tropical systems to CA
Yes but to limited extent
Likely still rare, just not quite as rare (still have to deal with reasons explained previously that aren’t conducive to tropical storms)
One of the constraints will weaken as ocean temps warm, no way CA waters will warm enough to really support tropical storm development but systems might decay more slowly
Events like Hilary could become more common
Less clear if other atmospheric variables would contribute (❓)
Not sure if anyone has studied this formally, would be interesting to ask this question more formally
Unlikely we’ll see a sharknado ;)
Hurricane Kay caused 109 MPH winds, could we see winds that high
This system (Hilary) could generate winds this high too, depends on trajectory and orographics
Winds could go as far as Venture and Santa Barbara counties
Winds will generate unusual rain patterns
Don’t think we’ve ever had a formal tropical storm watch or warning for CA, still seems unlikely but could happen (❓)
Will this bring strong wind event to NorCal
Possibly but uncertain at this point
Given forecast track, minor east-west differences in track could have big impact
Yes, no matter what though significant rainfall on east sides of mountains/slopes
Other locations the east-west movement could have big impact
Weather channel is forecasting 8-12 inches of rain in some areas east of SF and LA (❓)
Seems like overbroad characterization but some areas in extreme scenarios yes there’s a possibility
Upcoming El Niño
Will talk about this later, certainly still looking at it but other stuff going on now
The odds of a sharknado?
Above average but still unlikely (obviously joking)
How different is the impact of a tropical storm and winter storm
Heaviest rains fall in different places
Winds are coming from a different location
Eastern slopes and desert regions could see more rainfall than winter storm
Vegetation is also in different state (think deciduous trees), so wind impacts are different
Ocean conditions and swells will be coming from different directions
Airport closures in SD or LA with upcoming system?
Possible but hard to say at this point
Travel disruptions generally seem likely
Questions about risk of Maui-like downslope windstorm with arrival of this tropical system
Potential for moisture to make this less likely
Perhaps something to keep an eye on though, depends on how strong winds are and whether there’s any rain before the winds arrive
Don’t expect severe windstorm in NorCal
