Not sure what the real big difference between the two plots is, typhoon_tip. The hurricane heat content product is one that also takes into account sub-surface waters. Anywhere you see SSTs of ~27C or greater on the one map, you do see a non-zero (even if it is 1-10 kcal/cm^2) value of HHC; do note that the SST map only goes out to 60W (as noted in the header). However, those waters in the north Atlantic are only warm at the very top; the waters just beneath the surface are much cooler (<26C) and thus do not provide any heat content for the storm to use to maintain/increase its intensity. Waters in the Caribbean and Gulf, however, are warm to very large depths, bringing about very high values of HHC -- especially associated with the loop current and the climatologically warm waters in the NW Caribbean.