.  Temperatures  above  normal  at  sea  level, generally 26°C (79°F) or more in the lower layers. l Moisture above normal at all levels. l Westerlies greater than average, north of the latitude  of  the  seasonal  maximum. . Easterlies weaker than average in a wide zone. l Easterlies decreasing with height. . The latitude of the subtropical ridge is higher than  normal  above  the  500-hPa  level. l Evidence of a fracture in a trough aloft (at 200 hPa). .  Long  waves  that  are  slowly  progressive. . A zone of heavy convection is present, indicating the absence of the trade inversion. l An increasing surface pressure gradient north and  west  of  the  suspect  area. . The disturbance has relative motion toward the upper ridge at or above 400 hPa. Other Indications of Development Other  indications  of  development  are  sea  swell  and tide observations. Swells associated with a tropical storm will have a frequency less than average and an amplitude  greater  than  average.  The  normal  swell frequency is 8 per minute in the Atlantic and 14 per minute in the Gulf of Mexico. Hurricane winds set up swells with a frequency that can decrease to four per minute. The period of the swell will also be much longer than  usual. Swells  will  approach  the  observer approximately from the direction in which the storm is located. The swell height is an indication of the storm’s intensity,  especially  when  the  swells  have  not encountered shallow water before reaching shore. Abnormally  high  tides  along  broad  coastlines  and along shores of partially enclosed water bodies are also a good indication of storm development. The highest tides will normally be found to the right of the storm path, looking downstream. DETECTION Meteorological  satellites  have  greatly  aided  in  the detection  of  tropical  disturbances,  especially  during  the early  life  cycle. It is important for meteorologists, analysts,  and  forecasters  to  be  able  to  effectively interpret  these  pictures  to  extract  their  maximum benefit.  Through  proper  interpretation  of  satellite  data, determination of size, movement, extent of coverage, and  an  approximation  of  surface  wind  speed  and direction can be made. Satellites have become the most important method of detection of disturbances. Aircraft reconnaissance also plays an important role in  tropical  cyclone  detection  throughout  the  North Atlantic, Caribbean Sea, and the Gulf of Mexico. This has  become  even  more  important  when  used  in conjunction  with  the  data  from  satellites.  Areas  of suspicious  cloud  structure  can  be  investigated  by aircraft whose crews include trained meteorologists. These reconnaissance flights can provide on-station data,  either  high-  or  low-level,  that  would  not  be available  otherwise. Another  method  of  detecting  tropical  disturbances is through the use of radar. Present radar ranges extend about 300 miles and can scan an area approximately 300,000 square miles. The   Navy   and   NOAA   also   maintain   several different types of moored METOC buoys that report various meteorological and oceanographic elements. These stations send out measured data automatically or upon query. LOCATION The problems of formation, detection, and location are in reality a single three-in-one problem. One is dependent on the other. In the case of satellite pictures, reconnaissance, and radar  detection,  the  location  is  fairly  certain,  barring navigational  errors.    If  detection  is  made  through  the analysis, the exact location is more difficult to ascertain in the incipient stage of the storm, especially when the analysis is diffuse. The exact location should be decided upon only after the most intensive study of the data. The analyst should be prepared to revise his or her decision in the face of developments which are more conclusive. INTENSIFICATION Only when easterlies extend vertically to 25,000 feet or more at the latitude of the vortex is intensification possible.   This   most   frequently   occurs   when   the subtropical ridge lies poleward of its normal position for the  season.  The  following  characteristics  are indications  of  intensification: l Movement is less than 13 knots. 11-3