28 MANUAL OF MARINE METEOROLOGICAL OBSERVATIONS 



3400. WIND SHIFTS 



3410. GENERAL. Wind shift is the manner in which the wind changes 

 direction. It is generally considered an abrupt change in the wind direction 

 of at least 90 degrees. Wind shifts are associated with the phenomena charac- 

 teristic of a cold- front passage that are listed below: 



(a) Gusty winds shifting in a clockwise direction in the Northern 

 Hemisphere (south shifting to west, or southwest shifting to 

 northwest), and counterclockwise in the Southern Hemisphere 

 (north shifting to west, or northwest shifting to southwest). 



(b) Rapid drop in dew point. 



(c) Rapid drop in air temperature. 



(d) Rise in pressure. 



(e) In summer; lightning, thunder, heavy rain, and possible hail. 



(f) In winter; frequent rain or snow squalls with cloud heights changing 

 rapidly- -to either higher or lower heights than existed before 

 the wind shift. 



3411. When a fast vessel overtakes a slow- moving cold front, items (a), 

 (b), (c), and (d) of J3410 will occur in the reverse of the manner described. 

 For example, the wind will shift counterclockwise in the Northern Hemisphere, 

 and the dew point will rise rapidly. However, phenomena described in 

 items (e) and (f) may be encountered in the frontal zone. 



3412. Wind shifts may occur without precipitation, but they are usually 

 accompanied by strong winds. 



3420. ENTRY OF WIND SHIFTS ON FORM 615-5. Enter the time 

 (GCT) of wind shifts that occurred during the previous 6 hours in the column 

 headed "Remarks" on the line pertaining to the observation. Example: 

 Wind shifted SW to NW at 0835. 



3421. RADIO REPORTING OF WIND SHIFTS. Wind shifts that occur 

 during the six (6) hours prior to the standard ship's weather observation 

 should be reported. This information is to be added, in plain language, to the 

 regular coded ship's weather observation. EXAMPLE: SHIPS 40493 06612 

 62614 97216 06448 45420 56308 00347 12664 WIND SHIFTED SW TO NW 

 AT 0835Z. 



