Reading the Upwelling: Why Central California Went Blue While San Diego Stayed Green
- Bret Whitman
- Jun 30
- 11 min read
The week of June 15-21, 2026 showed California's coasts what upwelling actually looks like—and why it's the single most important oceanographic signal for divers to understand. While San Diego battled a stubborn surface bloom, central California experienced something rare and beautiful: a full-on upwelling event that drove Monterey and Big Sur to 40-50 feet of clarity. This wasn't luck or random timing. It was upwelling—the seasonal process that brings cold, nutrient-rich water from the deep ocean to the surface—and understanding how to read it, predict it, and hunt it is the key to mastering California diving.
WHAT IS UPWELLING, REALLY?
Most divers hear "upwelling" and think "cold water." That's partially correct, but incomplete. Upwelling is the physical process where deep ocean water is forced to the surface by wind and coastal geography. The cold water is just the signature. The real story is what that cold water brings with it: nutrients (nitrogen, phosphorus, iron) that fuel phytoplankton blooms.
Here's the paradox that confuses everyone: upwelling brings COLD, NUTRIENT-RICH water. Cold water itself is clear (molecules move slower, less scatter). But the nutrients feed plankton, which then blooms and turns the water green. So a successful upwelling event creates a contradictory signal: cold water + nutrients = plankton bloom = poor visibility.
Except when wind disrupts it.
If coastal upwelling is strong and the wind regime keeps the surface mixed, the plankton accumulation stays dispersed and visibility remains good. If the upwelling is weak or the wind dies, plankton accumulate in a surface lens and visibility crashes. The week of June 15-21 demonstrated this perfectly: offshore wind in central California kept the surface mixed (clear water), while in San Diego the wind pattern was different, allowing plankton to accumulate (murky water).
THE JUNE 15-21 UPWELLING EVENT: WHAT HAPPENED
The trigger: A Pacific high-pressure system sat offshore, driving strong northwest winds along the California coast June 15-19. These winds parallel the coast and force surface water away from the land. Deeper water rises to replace it—classic Ekman transport upwelling.
The geographic effect: Upwelling is strongest where the continental shelf is narrow and coastlines face north-south (perpendicular to the prevailing northwest wind). Big Sur and the Monterey Peninsula fit perfectly. San Diego's coast faces more southwest, making it less efficient for upwelling. Orange County's bays trap water, suppressing upwelling entirely.
The result:
Central Coast (Big Sur, Carmel, Monterey): Cold upwelled water (51-52°F at depth) was forced to the surface. Strong offshore wind dispersed any plankton bloom. Visibility climbed to 40-50 ft at Pt Lobos and deep sites, 30-35 ft at accessible reefs.
San Diego: Weaker upwelling signal. Surface water stayed warm (67-70°F) and trapped a plankton lens at the interface. Visibility remained 0-5 ft in shallow zones, improved to 8-15 ft offshore and at depth.
Orange County: Bays and coves trapped warm water. Upwelling was suppressed. Shallow areas saw 3-8 ft visibility. Deep reefs accessed from shore or via boat showed modest improvement (12-18 ft).
The temperature profile told the whole story: a sharp thermocline (boundary between warm and cold water) at 15-35 ft depth, with cold upwelled water below and warm surface above. Divers at La Jolla Shores who descended through the thermocline reported dropping from murky 65°F surface water into clear 51-52°F deep water—a dramatic shift in both temperature and visibility within seconds.
READING THE UPWELLING SIGNAL: HOW TO PREDICT IT
Upwelling isn't random. It follows predictable patterns based on wind, coastline geometry, and season. Learning to read upwelling forecasts is one of the most valuable skills for a California diver.
Wind Pattern Recognition
Upwelling-favorable winds blow parallel to the coast from the north (northwest in California). A persistent northwest wind forecast (3+ days) signals incoming upwelling. During June 15-21, the NOAA forecast showed sustained 15-20 knot NW winds from the 15th through the 19th—a classic upwelling setup.
Where to look: NOAA Marine Forecast (weather.gov), NDBC buoy data, or simple wind forecasts on any weather app. If you see "NW 15-20 knots, sustained" forecast for 3+ days, upwelling is coming.
Water Temperature Trends
Temperature is the thermometer of upwelling. As upwelling begins, at-depth temperatures drop. A water report that shows "surface 68°F, depth 56°F" shifting to "surface 68°F, depth 48°F" over a week indicates strengthening upwelling.
During June 15-21, central California showed the progression:
June 14 (before upwelling peak): 54°F at 30 ft
June 17 (mid-upwelling): 52°F at 30 ft, with some 50°F readings at depth
June 20 (peak): consistently 51-52°F at all depths below 20 ft
This cooling signal means upwelling is intensifying. More cold water is rising.
Visibility Trends (If Wind Pattern Supports It)
Here's the nuance: upwelling brings cold water + nutrients, which can feed a bloom. But if wind is strong and coastal mixing is high, visibility improves despite the bloom potential. Watch the combination:
Strong NW wind + upwelling = improving visibility (wind disperses bloom)
Weak wind + upwelling = stable or declining visibility (bloom accumulates on surface)
During June 15-21, central California had both (strong wind + upwelling), so visibility improved to 40-50 ft. San Diego had weaker wind + upwelling, so the bloom accumulated and visibility stayed poor.
NOAA Data Resources
Real data sources for upwelling prediction:
NOAA Marine Forecast (weather.gov): Wind speed, direction, persistence
NDBC Buoys (ndbc.noaa.gov): Real-time water temperature, wind speed, wind direction
ERDDAP (CoastWatch): Historical upwelling indices for specific coastal regions
NOAA Upwelling Index: Formally calculated metric for upwelling strength by coast section (monthly)
These are the actual tools oceanographers use. Learning to read them takes practice but is absolutely worth it.
THE MONTEREY PARADOX AND UPWELLING: WHY SUMMER IS BACKWARDS
This is where upwelling gets weird and where the June 15-21 event illuminates a critical pattern.
In winter, upwelling brings cold water to the surface, but short days, cold air temperatures, and dormant biology mean plankton blooms don't happen. Water stays clear.
In summer, the sun is high, days are long, and water is warm. If upwelling is active (it is—it peaks in spring/summer), it brings nutrient-rich cold water into warm, sunny surface layers. Perfect conditions for explosive plankton growth. This is why Monterey in summer is pea soup despite upwelling being strongest—the upwelling brings the nutrients that feed the summer bloom.
Central California during June 15-21 showed this in real time:
Upwelling was active (cold water rising, strong wind dispersing it)
Summer conditions existed (long daylight, warm upper layer)
Visibility was EXCELLENT (40-50 ft at Big Sur)
Why the contradiction? The strong offshore wind kept the surface mixed. Plankton weren't accumulating in a surface lens—they were dispersed throughout the water column. At depth, you're below the bloom accumulation layer anyway.
But if the wind had died or turned onshore, that same upwelling + summer nutrients would have produced a surface bloom within 48-72 hours. This is exactly what happened in San Diego: weaker upwelling, different wind pattern, bloom accumulated, visibility tanked.
The lesson: Upwelling in summer is a double-edged sword. The mechanism that creates clear water in the short term (nutrient delivery + wind mixing) can set up the conditions for a bloom within days if the wind pattern shifts. Plan accordingly.
GEOGRAPHIC PATTERNS: WHERE UPWELLING HITS AND WHERE IT DOESN'T
California's upwelling geography is not uniform. Some coasts are upwelling hotspots; others are suppressed.
Upwelling Hotspots (Strong Signal)
Big Sur / Pt Lobos / Carmel: Narrow continental shelf, north-south coastline orientation, exposed to open ocean. Peak upwelling intensity. Highest cold-water signal, best for productivity, most reliable for clear water when wind is favorable.
Cape Mendocino / Fort Bragg / Point Arena: Similar geometry to Big Sur. Strong upwelling.
Cape San Martin / Cambria / San Simeon: Secondary hotspot, slightly weaker than Big Sur but still strong.
Point Conception (Ventura/Santa Barbara boundary): Geography shifts here. Upwelling begins to weaken south of this point.
Transition Zone (Moderate Signal)
Santa Barbara Channel / Ventura: Moderate upwelling. Coastal topography begins to shelter the coast from pure north-south upwelling.
Malibu / Santa Monica / San Pedro: Upwelling signal present but modulated by coastal geometry and basin dynamics.
Suppressed Upwelling (Weak Signal)
Orange County Bays / Laguna: Bays trap water. Upwelling is weak or non-existent in confined water.
San Diego Bays / Mission Bay: Same suppression. Protected waters don't upwell efficiently.
Inside any lagoon or protected harbor: Upwelling signals are minimal.
During June 15-21, this geographic pattern was on full display:
Big Sur (hotspot): 40-50 ft visibility, cold upwelled water
Central Monterey (strong): 25-35 ft visibility
Orange County bays (suppressed): 3-10 ft visibility despite upwelling occurring offshore
If you're planning a trip during upwelling season, target the hotspots (Big Sur area) for maximum benefit. Avoid protected bays and lagoons—upwelling doesn't help them.
THE MARINE HEATWAVE TWIST: 2026 UPWELLING IN CONTEXT
The June 15-21 upwelling occurred within the larger 2026 marine heatwave context. Surface temperatures (67-70°F) are running 2-4°F above normal. At-depth temperatures (51-52°F) are within historical range. This creates an exaggerated thermal contrast.
What does this mean for upwelling dynamics?
Upwelled water stands out more: The 51-52°F upwelled water is colder than the 67-70°F surface. The thermocline (boundary) is sharper. Divers can literally see the boundary—murky warm water above, clear cold water below.
Bloom potential is higher: The larger temperature difference + abundant nutrients = more aggressive plankton growth if wind fails. The surface lens sits higher and thicker.
Upwelling-favorable windows are more valuable: When upwelling + favorable wind align, the clarity improvement is more dramatic (40-50 ft instead of 25-30 ft typical).
Planning is more critical: Upwelling patterns shift faster in a heatwave year. What's clear on Tuesday might be murky by Friday if wind patterns shift.
The June 15-21 event benefited from this: the strong upwelling brought exceptionally cold water (51-52°F, below normal), creating a sharp thermocline and exceptional clarity at depth.
TACTICAL DIVING DURING UPWELLING
For Shore-Based Hunters
1. Depth is your friend: During active upwelling with mixed surface conditions (like June 15-21 central CA), descend to access the clear upwelled water below the thermocline. Target 40-60 ft where the cold, clear upwelled water lives.
2. Know your thermocline depth: The thermocline (sharp temperature/clarity boundary) is typically 15-35 ft during summer upwelling. Descend past it. Time your dive to access the clear water below.
3. Hunt at Big Sur / Pt Lobos during NW wind forecasts: These are the upwelling hotspots. When upwelling-favorable winds are forecast, plan a trip here. Expect 30-50 ft visibility if the wind pattern holds.
4. Avoid bays and lagoons during upwelling: Upwelling is suppressed in protected water. During upwelling-favorable conditions, shallow bays stay murky while open coast clears. Know the difference.
For Boat Hunters
1. Timing is everything: Upwelling events are short (3-7 days typically). A boat trip during an active upwelling window (strong NW wind, cold water signal) will find exceptional conditions. Book when the forecast looks favorable.
2. Target offshore pinnacles when upwelling is active: Offshore sites benefit more from upwelling than sheltered coves because they're exposed to the full upwelling transport. Expect 25-35+ ft visibility during upwelling events.
3. Understand the post-upwelling collapse: After upwelling winds die (typically after 5-7 days), a "relaxation" period follows. Plankton bloom can intensify rapidly. Book your trip during the upwelling window, not after.
For Planning
1. Monitor NOAA forecasts for NW wind persistence: 3+ days of sustained NW 15+ knots = upwelling coming. Plan trips 1-2 days into this forecast window for peak conditions.
2. Track water temperature trends: Rapid cooling at depth signals strengthening upwelling. These are prime diving windows.
3. Scout real-time visibility reports: During upwelling windows, visibility changes daily. Check dive reports and forums before committing. A report from yesterday might be significantly different from today.
4. Understand your regional upwelling signal: Big Sur = strong upwelling, reliably clear during favorable wind. San Diego = weak upwelling, unreliable for clarity improvement even when upwelling occurs.
SPECIES IMPLICATIONS DURING UPWELLING
Upwelling affects fish distribution and behavior:
White Seabass: Prefer the upwelling boundary (thermocline). They hunt where the thermal change creates a sharp "edge" of productivity. During active upwelling (like June 15-21), white seabass move into upwelling zones. Offshore or deep reefs during upwelling = white seabass potential.
Calico Bass: Year-round residents, distributed across depth zones. Upwelling doesn't trigger migration, but improved visibility = better hunting success.
Halibut: Prefer sandy-rocky transitions at moderate depth (20-50 ft). Active upwelling with clear water at depth = excellent halibut habitat and hunting.
Rockfish: Abundant at depth. Upwelling brings clarity to deep reefs, improving rockfish hunting opportunities.
Leopard Sharks: Seasonal inshore residents. During upwelling, schooling becomes more visible (you can see them). The June 15-21 upwelling brought leopard sharks back onto the Marine Room reef, likely because improved visibility made hunting more viable.
Yellowtail: Pelagic migrants. Upwelling events can trigger foraging activity by increasing productivity. June 17 (mid-upwelling) yellowtail bite at La Jolla Kelp was "wide open"—partly timing (early morning window), partly upwelling-driven productivity.
THE FORECAST GAME: PREDICTING THE NEXT UPWELLING
As of late June 2026, the question is: when's the next major upwelling event?
Historically, coastal upwelling peaks in spring (May-June) and moderates in summer (July-September). The June 15-21 event was strong but not exceptional. Mid-to-late July might see weaker upwelling signals as the seasonal pattern transitions.
However, the marine heatwave is disrupting normal patterns. The strong thermal contrast (warm surface, cold at depth) might amplify future upwelling events. Monitor:
NOAA wind forecasts: Sustained NW 15+ knots = next upwelling event
Water temperature reports: Rapid cooling at depth = upwelling intensifying
Visibility trends: If visibility improves after poor conditions, upwelling is clearing it
The next significant upwelling opportunity might not arrive until late July or August. Plan accordingly.
THE BIG PICTURE: UNDERSTANDING UPWELLING TRANSFORMS YOUR DIVING
The divers who succeeded during the June 15-21 upwelling event were the ones who understood what was happening: upwelling was strong, wind was dispersing the bloom, cold clear water was rising, and it was a temporary window. They planned trips to Big Sur, Monterey offshore sites, and deep reefs. They descended past thermoclines. They timed their dives to the weather forecast.
The divers who got frustrated were the ones expecting San Diego coves to magically clear during upwelling season—they didn't understand that upwelling is suppressed in bays and lagoons, or that upwelling brings nutrients that feed blooms, or that the same cold water upwelling that creates clarity can set up a bloom within days if wind patterns shift.
Upwelling is not "good" or "bad." It's a mechanism. Understanding how to read it, predict it, and exploit it is the difference between a great California diving trip and a wasted vacation.
UPWELLING CHEAT SHEET
Signs of active upwelling:
Sustained NW winds 15+ knots for 3+ days
Water temperature drops 3-5°F at depth
Visible thermocline (sharp temperature boundary)
Cold upwelled water (51-56°F) visible below warm surface
Best places for upwelling clarity:
Big Sur / Pt Lobos (hotspot)
Offshore sites during upwelling window
Deep reefs (40-60 ft) accessed from shore
Worst places during upwelling:
Bays and lagoons (suppressed upwelling)
Shallow coves in Orange County (protected from upwelling)
Anywhere if wind shifts to calm (bloom sets up quickly)
Timing strategy:
Monitor NOAA forecast for NW wind persistence
Book trips 1-2 days into forecast window
Avoid trips on day 5+ after upwelling start (relaxation and bloom onset)
Plan for 30-50 ft visibility offshore, 20-35 ft at shore-accessible deep reefs
Species advantage:
White seabass = upwelling edges
Halibut = upwelling-cleared deep sand
Yellowtail = upwelling productivity
Leopard sharks = upwelling schooling visibility
This post is based on the June 15-21, 2026 upwelling event documented across California's coasts. Data sources: NOAA Marine Forecast, NDBC buoy network, SpearFactor dive reports, and real-time field observations. Water temperature, wind, and visibility trends compiled from June 14-21 reports. Photo credit: NOAA satellite oceanography, water profile data from NDBC.
Image credits: coastal/equatorial upwelling diagram by ReddKing (CC BY 4.0); Point Lobos kelp forest by Lt. John Crofts, NOAA Photo Library (public domain); white seabass by Patrick Cox via iNaturalist (CC BY 4.0); leopard shark in kelp by Matthew Field (CC BY-SA 3.0); kelp bass by Steve Lonhart / MBNMS (public domain). All images via Wikimedia Commons.
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