1 The Gulf Stream Near the Rhumb Line Newport-Bermuda June 12, 2018 An Analysis of Conditions W. Frank Bohlen ([email protected]) Mystic, Connecticut Clouds continue to limit satellite views of the Gulf Stream allowing typically one or two quality instantaneous images each week. The frequency of composite views is only slightly better. The last available image of 9 June shows the north wall of the main body of the Stream crossing the rhumb line at a point approximately 200nm from Newport (Fig.1). The resulting flows are proceeding from the southwest to the northeast across the line. To the north there is a mass of warm water apparently “shed” from the Gulf Stream much in the way that winds displace waters from the crest of a breaking wave. The resulting distribution of warm water will produce some flows prior to the entrance to the main body but speeds are expected to be low most probably below 1 knot. The crest associated with this mass of warm water is part of the meander that has affected flows along and across the Newport- Bermuda rhumb line for more than a month. Over the past 10 days the wavelength of this feature has increased significantly with the trough now positioned nearly 120nm to the east of the rhumb line. The sequence of four (4) day satellite ( GOES 16) sea surface temperature (SST) composites from the Ocean Prediction Center nicely documents this evolution and provides a valuable indication of the possible rates of change of meanders as well as the overall evolving form of the north wall of the Gulf Stream. https://ocean.weather.gov/Loops/ocean_guidance.php?model=GOES&area=MidAtl&plot=sstrec&day=0&loop=1 (Also, compare Fig 2 to Fig.3). Examination of the altimetry based model results for June 11 (two day delay required for data analysis) (Fig. 4) shows flows crossing the rhumb line at near right angles or at a much less acute angle than indicated by the June 9 SST composite image (Fig.1). The difference , most likely due to the presence of the warm water mass north of the main body of the Stream, suggests that significant east going current will be encountered to the north of the maximum water temperature gradients in the vicinity of 38 o 30’N. This is a relatively unusual condition. The altimetry based model shows the main body flows affect a well defined region extending for approximately 30nm along the rhumb line (Fig.4). To the south of this area flows are variable becoming progressively more west going by 38 o N. These westerly flows appear to be part of a counter-clockwise
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The Gulf Stream Near the Rhumb Line Newport-Bermuda June 12, 2018
Figure 5 NOAA Numerical Model of Sea Surface Temperatures ‐ June 9, 2018Black Line Shows Newport‐Bermuda Rhumb Linehttp://polar.ncep.noaa.gov/global/monitor/
http://polar.ncep.noaa.gov/global/monitor/
Figure 6 NOAA Numerical Model Gulf Stream Surface Currents ‐ June 9, 2018Yellow Line represents Newport‐Bermuda Rhumb Line