Disturbance in the Gulf

The disturbance in the southwestern Gulf of Mexico is forecast to start moving north tomorrow with a 70% chance of cyclone formation in the next 48 hours.  Lets take a look at the oceanographic conditions in front of the storm.

First we have the SST maps from our two operational models, the NOAA RTOFS on the left and Navy GOFS on the right.  The surface waters of the western Gulf are warmest, with a large area in the northwester Gulf above 29C.  GOFS looks to be slightly warmer than RTOFS at the surface. The color-filled circles represent the locations of recently surfaced Argo float profiles.

Looking at the temperature at a depth of 200m, we see a large area of colder water below 15C in the northwestern Gulf.  Highest surface temps, lowest temps at 200 m, means significant stratification in this region.  At 200 m you can better see the mesoscale structures.  Each model has the extended Loop Current, and that band of warm water stretching diagonally across the Gulf from northeast to southwest.  The warm band exists in both models, but the mesoscale structure has differences.

Last map comparison is the surface salinity. Lots of fresh water from the Mississippi River in both models along the northern Gulf coast, extending way offshore in the northwester Gulf, again increasing the stratification.

Now a quick look at the Argo floats.  We’ll publish the orange float #4902916, the most western one on the map.   Here we zoom into the upper 400 m, the region where we often see the largest differences between the model profiles.  The float data is in blue, RTOFS green, and GOFS orange.  Temperature profiles are in good agreement between models and data, with GOFS slightly warmer at the surface and closer to the float observation. GOFS tends to follow the Argo profile quite closely. RTOFS tends to be a bit warmer below the surface mixed layer and a bit colder at 150 m.   Salinity is similar with GOFS tending to follow the profile more closely, and RTOFS a bit fresher at depth and a bit saltier near the surface.  Neither model is getting the very low salinity observed in the freshwater surface barrier layer.

So what dis we learn about oceanographic conditions in the Western Gulf where the current disturbance may be headed?  The  north western Gulf surface waters are the warmest in the Gulf, above 29C, and the western Gulf is highly stratified with cold water at depth and low salinity water at the surface.  The stratification acts to inhibit mixing and cooling of the surface water.  If the winds are sufficient to overcome the stratification, there is a large source of cooler water less than 40 m below the surface that could help rapidly cool the surface water.  We have the possibility of two gliders, a Navy glider and a TAMU glider to be in place to capture the response if this develops.

Last 5 posts by Scott Glenn

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