From June through November, no fishing trip is complete without a nod to hurricane season—especially as we head into fall. Stormy weather has an effect not only on the atmosphere but also on the water—and on the fish that inhabit it.
While many people envision a perfect day of fishing as sunny skies of breezy blue, it might be the cloudy gray days of incoming rain that have experienced anglers dreaming of fish that bite hard and fast. Hurricane season can bring hurricanes, but it can also bring the messy weather that makes fish want to belly up to the bait. All you have to do is watch the barometer and understand what that means for fish.
A barometer is a weather instrument that measures the atmosphere’s air pressure—how thick the air is above you and whether it’s rising or sinking. Readings are measured and given in millibars or inches of mercury at sea level. For reference, standard pressure at sea level is considered 29.92 inches of mercury or 1013.2 millibars. Measurements above the standard are considered high pressure numbers while measurements below the standard are considered low pressure.
High pressure barometric conditions are often the result of fair weather. The air is thick and sinking, pressing down and drying out everything below it.
Low pressure barometric conditions are often the result of rainy or stormy weather. The lower the pressure, the stormier conditions become. The air is lighter and rising, lifting as it releases condensation and precipitation.
For anglers, what’s important to know is that regardless of the starting point, drops in barometric pressure make fish bite and often offer perfect conditions for great fishing while rises in barometric pressure seem to kill fish appetites and can leave your line untouched.
If you’ve ever watched birds mob a feeder before bad weather, a barometric drop over the ocean yields a similar fishy phenomenon. At sea, however, because it’s a watery environment that’s delicately balanced, more variables are in play that can affect the sea life we seek there. Here’s how it all works together.
Large bodies of water are highly complex environments—often enormous in scale—yet they’re extremely vulnerable to the elements of weather. As air masses move across the ocean unimpeded, their strength can impact everything from the fish themselves to every dimension of their surroundings.
Fish Barometers—Fish are highly sensitive to changes in their environment. It’s how they survive. All fish have lateral line systems—organs that detect even the slightest movements and pressure changes in the water around them. Many species of bony fish also have a swim bladder—a gas-filled chamber that controls buoyancy and helps a fish maintain a particular depth.
Even though fish are under the water, air pressure above also affects the air pressure in the swim bladder. To what degree depends on the species. For example, red grouper, black sea bass and gag have large swim bladders. In contrast, sharks, flounder, cobia and mackerel are examples of fish that don't have a swim bladder and are less vulnerable to air pressure changes.
Water Temperature—Science gives us a tidy way of layering a body of water by temperature and density. It’s called the thermocline, and it basically defines the boundaries of survivability for various species.
At the ocean’s surface, for example, the water is warmer thanks to the sun. The depth of this warm mixed-water layer varies seasonally, at its warmest and deepest in late summer to early fall.
Below the warm-water layer lies cold water all the way to the bottom.
The thermocline is basically the physical line where water dramatically changes in both temperature and often density, shifting from warm to cold and less dense to more dense.
While oceans can have multiple thermoclines as you descend into the deep, it’s the first one—the one defining the depth of the warm mixed waters—that plays a role in hurricanes. The deeper that warm layer is, the more fuel there is to evaporate up and into a hurricane that will increase in strength as it collects more and more warm water.
If a storm or hurricane unleashes its strength, the forces can be strong enough to breach the thermocline and churn warm waters into cold and cold waters into the warm layer. This can be problematic as most fish have evolved to inhabit certain depths and developed adaptations to suit certain temperatures.
Cold water typically contains more dissolved oxygen than warm water. Fish tend to move more slowly and need less food.
Warm water typically contains less dissolved oxygen than cold water. Fish tend to move more quickly and need more food.
So, if water becomes too warm for a species, it may not be able to breathe. Likewise, if water becomes too cold for a species, it may reduce its food intake.
Wind—Wind is how air masses and fronts move. Prevailing winds cause currents in the ocean and other bodies of water. Shifting winds cause eddies and mixing. When winds have sufficient force, the energy is driven down into the ocean and can cause mixing of the layers. The size and force of waves depend on aspects of the wind involved:
Speed—Slow wind speeds yield only small waves, for example, but as wind speeds increase, waves can too.
Duration—Short bursts or puffs of wind are typically too short-lived to make significant waves, but when durations become extended, waves can grow.
Fetch—Fetch is the expanse of open water wind can travel across without obstruction. The longer the fetch, the greater the impact wind can have on the water’s surface.
With hurricanes, the impact on currents can reach hundreds of feet deep. A long fetch of strong winds around the hurricane will push water in front of the hurricane as storm surge. Strong storms can push water inland, and shallow areas can be especially affected as strong currents stir up sediment and turn water turbid. Inflows of salt water may even shift not only water levels and currents but also salinity levels, bringing in fish that might not normally inhabit the shallower areas.
These shifts can also affect the levels of dissolved oxygen available to fish. Sediment raised from the bottom and storm debris combined with cloudy skies can block sunlight and result in fish kills due to lack of oxygen. Surges may also wash toxic residues that normally remain onshore, for example, into the water or breach manmade facilities only to release contaminants into the water. Additional dangers can emerge as bottoms change. Sandbars may form, channels may be altered, and wreckage or other debris released by the wind and currents may be near the surface yet not be visible due to the water’s turbidity. Fish may have difficulty seeing as well, and may not respond to lures or bait in more subtle colors.
Rain—You may think that a bit of rain has little impact on the vastness of the ocean, but researchers are finding that the fall of fresh water—rain—does have an impact on salinity, the churn of the ocean in a strong storm and the ability of the storm to grow.
Studies by the Department of Energy and the National Oceanic and Atmospheric Administration have found that since fresh water is lighter than salt water, rainfall often remains on the surface of the warm layer of mixed waters in the ocean. It can actually block colder water from being churned to the surface, where that colder water might slow down a storm. Instead, the fresh water on the surface can fuel a storm as it evaporates readily and is gathered easily. In fact, researchers have found that decreases in salinity resulted in larger, stronger storms.
In shallower waters, rainfall can wash runoff, debris and contaminants into the water. Rain can also result in additional nutrients or food sources entering an environment. In heavy downpours, fresh water may spread across the surface of salt water and change salinity levels in shallower areas. As a result, fish may swim deeper, gather to feed or migrate to areas with more compatible salinity levels.
Whether you follow the intricate rules of meteorology or the knowledgeable voice of the experienced angler, the message is the same.
As bad weather approaches, the barometer drops, and the fish want to feed.
Once the bad weather passes and the barometer begins to rise, the fish will stop biting—or at least be more challenging to catch.
So, how do you know how to time it? As with everything else, it’s nuanced. The barometer typically begins dropping for a hurricane 12 to 24 hours before storm arrival. However, changes in the barometer can happen quickly, slowly or somewhere in between and are measured in millibars or fractional inches of mercury—in Hg.
Rapid changes involve increases or decreases of more than 0.18 in Hg in less than three hours.
Slow changes involve increases or decreases of 0.003 to 0.04 in Hg within three hours.
If changes are less than 0.003 in Hg in that timeframe, the pressure is holding steady.
As a rule, the longer it takes the barometer to change, the longer the weather will last. Likewise, the faster and deeper the drop, the stronger the storm will be. In some cases—like a quick cloudburst—the weather event may be so brief that the barometer doesn’t change at all.
To be clear, an actual hurricane is no place to be, and even an everyday storm can bring lightning, heavy rains and winds that can grow deadly. NOAA’s National Ocean Service cautions that at sea, a hurricane can generate 60-foot waves and rough undercurrents that can reach 300 feet deep.
At the surface, the results can endanger humans and capsize or destroy water craft.
Below, even sea life is at risk. Currents can be strong enough to shift sand, break up coral reefs, cloud the water, and change salinity and temperature levels too rapidly for sea life to adjust. If water becomes turbid—saturated with sand and dirt—organisms that use sunlight to release oxygen into the water can’t do their job, and low oxygen levels can result in fish kills.
Offshore, weather can be unpredictable. As weather moves across water, warm surface temperatures can add moisture and power to a brewing storm. What begins as squally weather or a mild tropical depression can—given the right conditions—build into a tropical storm or even a hurricane. Always pay heed to and obey all marine advisories and warnings.
The takeaway is that hurricane season typically offers plenty of opportunities for some great fishing, but anglers have to be prepared for anything—before, during and after a weather event. Weather can be quite changeable on the water, but the fish know what they need to do. To find them, you need a captain and crew that understand the weather and know what the fish know.
There’s no better place to find that captain and crew than on the Louisiana Charter Boat Association’s website. Start exploring, and see the wide variety of experience and expertise available to you. It may be hurricane season, but some of the best fishing trips ever are all thanks to a spot of iffy weather and a sweet little barometer drop.
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