|
Understanding, utilizing and benefiting from sea surface temperature charts
Tech support courtesy of Terrafin Software.
An increasing number of successful blue water anglers are taking
advantage of sea surface temperature data to stack the odds in their
favor. Let’s take a peek at this modern day technology and see how it
can help us.
To kick things off, let’s discuss where sea surface temperature data actually originates. The raw data utilized in almost all commercial sea surface temperature services originates from NOAA polar orbiting weather satellites, known as POES (Polar Operational Environmental Satellites). Each POES satellite provides daily shots for each part of the globe. At the present time, there are 5 POES satellites which are capturing usable data for our purposes, some more reliably than others.
The various instruments on POES capture a variety of information. The data used in the calculation of sea surface temperatures is created by advanced very high resolution radiometers. The data is transmitted to earth in a format called HRPT or high resolution picture transmission, where it’s captured by specialized receiving systems. A number of commercial chart companies operate their own ground receiving stations to retrieve the data and in recent years the National Oceanic & Atmospheric Administration has made the raw data captured by their own ground stations available for public use.
OK, that was boring. Anyhow, that’s where it all starts.
Now that the raw data has arrived on earth, what’s the next step? Each morning and evening sea surface temperature providers such as Terrafin Software, begin downloading all the satellite data from the last 8-10 hour period. Usually, the best satellite shots are taken from midnight to around 7:00 AM. Using specialized imaging software, the automated task of processing each pass is now undertaken. During this process the data is calibrated and temperature values are calculated. Clouds tend to show up in the raw data as cold water, which evidently can make for some fairly misleading temperature charts.
A number of tests are performed to determine what percentage of the data is actually useable. Cloud pixels are marked as un-useable and are often shown as white on completed charts. It’s at this stage that the data is automatically navigated to insure that the temperature data is aligned with the correct geographic coordinates. This is a tricky process with varying degrees of success. Up to this point, all of the processes are done automatically using technologically advanced imaging software.
It’s at this stage in the game when commercial sea surface temperature providers actually earn their keep. As mentioned, the imaging software attempts to navigate the data to the proper ground coordinates. Unfortunately, this doesn’t always work as designed and viewers frequently end up with charts that are one to ten miles out of alignment and even as bad as twenty to thirty miles off! Often, this error is utterly obvious but on other occasions the mistakes can be difficult to spot. A more accurate alignment is possible but requires manual intervention and is time consuming. It’s a critical step in creating accurate sea surface temperature charts and most professional services do spend the time necessary to ensure that the alignment is as accurate as possible. While being a mile or two off might not ruin your day, running 50 miles out in sloppy seas to a temperature break which in all reality is twenty five miles away from where you expect it to be, can be a bit frustrating.
There are a number of institutions which do create sea surface temperature images from the raw data and make the images available to the public at no cost. The most widely used sites for this type of free information would be Rutgers University, Johns Hopkins University and the various NOAA Coastwatch sites. This info may be off, so be careful.
Cloud cover is actually another factor in the creation of accurate sea surface temperature charts that benefit’s from manual intervention. While the imaging software can automatically identify much of what is considered to be clouds, often times areas of cover slip through all the tests. In these cases, the cloud cover most often shows up on a temperature chart as cold water. Like I said earlier, on occasion this is obvious to the user and on other occasions it is not. Professional services who review the raw data on a daily basis quickly recognize when they’re looking at clouds verse actual cold water. When areas of cloud cover slip through the initial tests, they manually remove those pixels from the chart. Better to show you nothing, than to send you out on a wild goose chase.
Now that the calibrated raw data has been properly aligned, professional services turn to their own proprietary software systems to create finalized viewable charts. With their technologically advanced software, they define and create individual regions while extracting the temperature values from the overall dataset and colorizing them to represent the temperature variances. Different services use different methods to show temperatures. Some prefer contour lines while others overlay the temperature directly on the chart. At Terrafin, they use color to show temperature differences as this creates an easily understood and very clear picture of where the temperature breaks are located. To get the best resolution from the colors, they’ll vary the temperature range from region to region and even from day to night. The goal is to use the smallest range possible within that specific region. Once the proper temperature range is determined, the chart is colorized and blown up to a set size. Bottom contours and various local reference points are added to the chart along with a Lat/Lon grid. The finished product is uploaded to a website where it is available to subscribers.
When a subscriber accesses the online charts, additional tools are accessible. When viewing a chart, users can move the mouse and get specific Latitude / Longitude readouts for that particular location. Viewers also have the ability to click on a particular point in order to set an origin, by moving the mouse the exact distance and heading from the specified origin will be displayed, a nice touch when setting up trolling patterns. Finally, there’s a chart loop tool which allows users to run the last 7 shots in sequence. This helps identify water movement trends. It takes a clear stretch of weather for this tool to work well, but during those periods it can be invaluable. So now that all of that is said and done, let’s get to the good stuff.
Utilizing sea surface temperature charts to increase your odds of success when heading offshore.
It’s common knowledge that the location of game fish is primarily affected by two factors, comfort and available forage. Water temperature can be the determining factor for both. Every species of offshore game fish has a comfortable temperature range they prefer. Too far above or below this range and the targeted species will seldom be located.
Sea surface temperature charts provide offshore anglers the ability to study an area and specifically target locations containing optimal water temperatures. After studying a temperature chart and heading to a particular location, anglers can pinpoint the actual temperature breaks by keeping a close eye on their temperature gauge and by keeping a sharp eye out for surface structure.
The most common surface structure associated with temperature variances are known as rips. Rips are visible disturbances on the oceans surface which appear to be long, narrow stretches of calm water paralleled by rougher water. Rips form at or near temperature breaks. The temperature break along a rip is referred to as a soft edges when the variance across it is less than 1_F and a hard edge when the temperature variance is above 3_F. Hard edge rips are more pronounced as they produce rougher water and are more easily identified than ‘softer’ edges.
A variety of blue water species tend to gather along these temperature rips for several reasons. Plankton gathers along temperature breaks and lays the groundwork for the initial stages of the food chain and in turn attracts bait to the area. As a general rule, plankton tends to concentrate on the cooler side of a rip. This is mainly because coastal water has substantially greater nutrient content and lower salinity than Gulf Stream water. The higher nutrient content provides plankton with an ongoing food source. In addition, the higher salinity level on the Gulf Stream side makes the warmer edge denser than the cooler coastal side. This denser water creates a sort of barrier which the free flowing plankton doesn’t cross. Because plankton and the nutrients on which they feed tend to cloud the water, sight oriented hunters such as marlin, tuna and wahoo tend to prowl the warmer, Gulf Stream side of rips.
Temperature boundaries, especially hard edges, act as a wall when the temperature on one side falls within a game fish's comfort range and the temperature on the other side does not. Predatory species will tend to swim along these edges rather than crossing them. Along with temperature differences, Sargassum weed and other floating debris often gets trapped in the calm area of rips, making the area even more inviting for game fish. It’s no secret that floating debris attracts bait and inevitably concentrations of bait attract predators. Shade from floating debris offers the added benefit of being an attractant, especially to dolphin.
After fishing any rips encountered along the edge of the Gulf Stream, it’s often advantageous to continue running east and searching for subsequent rips. Paying close attention to the offshore rips that are coupled with floating debris and/or bait will often pay off big. If radio chatter reports a solid formed weed line in a particular area, there is a good chance that there’s a temperature break there as well and the location is probably worth investigating. Remember that things are usually moving pretty quick offshore and it’s not uncommon to encounter a five knot current on the western edge of the ‘Stream, so work the area systematically and thoroughly. The most productive temperature rips are often those which have formed over highly defined bottom structure. These rips should never be ignored
Keep in mind that not all temperature rips or weed lines hold game fish. Always approach an area stealthily and look for bait or other signs of life before beginning to fish. If you intend on trolling the area, lures should be pulled parallel to the edge. Taking into consideration that the Gulf Stream flows north and most game fish tend to prowl with the current, troll in a northerly direction which will add a natural characteristic to your lures. However, any rips or weed-lines encountered along the western edges of fingers or warm water eddies should be trolled in a southerly direction as the currents in these areas move in a counterclockwise fashion. Speaking of fingers and eddies, lets take a closer look at these types of temperature breaks.
Fingers are actually small pockets of warm water which have edged their way west from the Gulf Stream. A finger of warm water is unique in that it stays connected to the ‘Stream. This connection continuously feeds warm water into the finger as the Gulf Stream continues to move north. The rate at which a finger of warm water moves depends on the size of the finger and how far it’s dwelled from the edge of the ‘Stream. As mentioned, the current in warm water fingers moves counterclockwise around its edges which means the water on the western edge of a finger is actually heading south.
Fingers which have gotten stuck and have actually stopped moving north are known as backflows. Backflows can stay in place for several days and are likely to grow as they stretch farther south while the Gulf Stream continues to push north. Similar to warm water fingers, currents in backflows move in a counterclockwise direction.
Eddies on the other hand are pockets of warm water which are completely surrounded by cooler water. Warm water eddies form when a portion of a finger dislodges from the Gulf Stream. Eddies tend to be round and contain warm water which circulates counterclockwise. You’ll find the warmest temperatures in the deepest part of an eddie which is around its edges.
Along with warm water eddies, it’s not uncommon when studying a temperature chart to notice cold water eddies. Cold eddies are pockets of cool water surrounded by warmer water. Contrary to warm water eddies, cold eddies are deepest and coolest at their centers. In your quest for consistent offshore success, cool water eddies should be avoided.
By now it should be obvious that warm water fingers, backflows and eddies all draw comfortable water temperatures west of the Gulf Stream and closer to shore. This is especially significant from late fall through early spring when water temperatures west of the ‘Stream can be relatively low. Game fish inhabiting the western edge of the Gulf Stream will often be found searching for prey in these warmer surroundings. As previously mentioned, rips often form along the edges of these warm concentrations and a quality pair of marine binoculars can make located them a bit easier.
The western edge of fingers, backflows and warm water eddies tend to hold the most productive rips. Study your temperature chart closely and start fishing near the western edge of any concentration of warmer water. Look for additional rips while heading toward the epicenter of the warm water. When a promising rip is identified, concentrate your efforts hard on that specific area. Troll along these well identified rips toward the south, following the counterclockwise current. This technique will provide you with a natural presentation since both bait and game fish tend to move with the currents. Pointing your bow south will keep you headed toward the tip of the finger or eddie, which may prove to be another productive area.
Remember that ideal water temperature is relative and varies from season to season and species to species. Subscribing to an online sea surface temperature chart service may not be for everyone. But if you ask any professional tournament angler his opinion, I know they’ll say the information provided is one of many valuable tools they use to give them the edge.
SPECIES LOW HIGH OPTIMAL
Blackfin Tuna 70 82 Mid 70’s
Yellowfin Tuna 64 80 Low 70’s
Blue Marlin 70 88 High 70’s
Bonito 62 82 Low 70’s
Dolphin 72 82 Mid 70’s
Kingfish 68 88 Mid 70’s
Sailfish 70 80 Mid 70’s
Spanish Mackerel 68 88 High 70’s
Wahoo 71 85 Mid 70’s
Cobia 68 80 Mid 70’s
|
