found from Ambrose lightship southward, Emd 

 the weakening of the temperature barrier 

 ordinarily found off Cape Hatteras, as indi- 

 cated by the extension of the 48° F. isotherm 

 all the way to Savsuinah. During this same 

 period, January through March, temperatures 

 at Portland and Boston remained slightly 

 above the mean. 



This pattern of surface water tempera- 

 ture closely parallels and is evidently 

 related to meteorological conditions during 

 this time. A high pressure cell in the 

 Greenland-Baffin Land region during January 

 and February and over Hudson Bay in March 

 presented a block which deflected polar air 

 southward across the east coast, bringing 

 abnormally low temperatures (Ludlum 1958a 

 and b). Maine and at times New England, 

 however, experienced occasional incursions 

 of moist, maritime air from the east and 

 northeast, producing above normal tempera- 

 tures £ind precipitation during both Janueiry 

 and March. 



The extremely low surface water temper- 

 atures seen at Diamond Shoals and the marked 

 weakening of the temperature barrier there, 

 indicate the dominance of Virginia coastal 

 water over Gulf Stream water in the region. 

 The reasons for this dominance caxmot be 

 definitely described at this time; a likely 

 conjecture is that above-normal precipita- 

 tion and runoff from November through May 

 (Monthly Weather Review) contributed to a 

 pressure gradient stronger than usual, which, 

 combined with a marked northerly component 

 of wind direction, gave added volume and 

 strength to the southward movement of 

 coastal waters. 



In general, winter conditions for 1958 

 resembled those for 1956 except that the 

 temperatures fell even lower and the cold 

 persisted longer, while 1957 was character- 

 ized by a warm winter. 



From Five Fathom Bank northward warm- 

 ing was slow and values fell below the mean. 

 Summer readings were slightly below "normal". 

 From Winter Quarter Lightship southward, 

 however, warming was rapid after the severe 

 winter and summer temperatures were near or 

 above the means at the various stations. 

 Maximum temperatures occurred in August at 

 all stations except Nantucket. 



From Cape Hatteras northward cooling 

 was in advance of the mean except during 



November, when air temperatures were 

 anomalously high. During December surface 

 temperature declined sharply as did air 

 temperatures. 



The three years of data from the light- 

 ship progrEtm so far accumulated indicate a 

 gross relationship between anomalies in air 

 temperature and in water temperature over 

 the eastern continental shelf. This is to 

 be expected near a windward shore where con- 

 tinental air masses flow seaward. Generally 

 speaking, the relationship appears to be 

 closer during the winter months, a period 

 characterized by strong winds, low relative 

 humidity and increased evaporation at the 

 surface. During the period of thermocline, 

 winds are weaker and relative humidity 

 greater, while such factors as radiation and 

 cloud cover become more importcint as the 

 season progresses. Hence the relationship 

 between anomalous air and water temperature 

 is less apparent during the summer. 



Bottom Temperature (Figure 1) 



During the nearly isothermal conditions 

 of winter, bottom temperatures reflect sur- 

 face conditions, exhibiting only a slight 

 lag in chilling. Thus in 1958 bottom 

 minima, like the surface values, was low. 



As was the case at the surface, the 

 temperature barrier usually found at Diamond 

 Shoals was weakened, and water less than 

 50° F. extended southward to Savannah. Dur- 

 ing the two previous winters the 50° iso- 

 therm fell at or slightly north of Diamond 

 Shoals. 



Warming at the bottom is a steady pro- 

 gression parallel to surface conditions up 

 to the time the thermocline is formed. Once 

 a temperature gradient appears, bottom tem- 

 perature is modified, sometimes abruptly, 

 by the prevailing weather, with wind the 

 governing factor. 



Bumpus (1957) described an intrusion 

 of cold water near the bottom in July 1956, 

 at Five Fathom Bank, Winter Quarter and 

 Chesapeake Lightship stations following a 

 period of preponderant strong southerly 

 winds. Similar conditions appear in early 

 July of 1957 (Day 1959) and again in 1958. 

 On the basis of three years of data it 

 appears safe to consider this advection 

 normal for the season, as was suggested 

 earlier by Bumpus. 



