FIG. 1. Observed and hypothetical soundings in Hurricane Gilbert. The light horizontal lines are isobars, those sloping upward to the right are isotherms, those sloping upward to the left are dry adiabats, and the nearly vertical ones are moist adiabats. The heavy solid and dotted lines indicate the soundings. (a) Soundings observed as Gilbert's pressure was falling rapidly before it attained its lowest value (solid) and after the lowest value when P_s was steady at a somewhat higher value (dotted); (b) two hypothetical soundings used to extrapolate surface pressures: IS, in which temperature and dewpoint vary linearly between flight level and values assumed for the surface (dotted), and IT, in which the lower part ofthe sounding is saturated and follows a moist adiabat from P _s to P _s and the upper part interpolates linearly from P _t to flight level (solid).