Supertyphoon Nepartak traveled for several days in the Northwest Pacific until it struck Taiwan on July 8, 2016. Wind gusts over the open ocean on July 8th were forecast to exceed 200 mph, although no measurements could be made at the surface at that time. Along its track in Figure 1, Vaisala’s Global Lightning Dataset GLD360 network detected a unique signature consisting of lightning in the eyewall that is located directly along and near the track of the center. While this signature has been observed in a few storms for up to 24 hours since GLD360 data became available in 2011, none of the storms had this feature that lasted nearly as long as the 72-hour period in Nepartak (Figure 1). It shows lightning enveloped along the track, a phenomenon which is being observed only to occur in very strong tropical cyclones that lack outer rainbands. Further studies are planned of the few other storms since 2011 that had a least a few hours of this signature. The ability of GLD360 to track lightning continuously far from land makes this type of observation possible. Satellite imagery in Figure 2 shows an intense tropical cyclone with a sharply defined eye within a uniform circular annulus, but no outer rainbands.
FIGURE 1. Map of track and GLD360 strokes for supertyphoon Nepartak in North Pacific Ocean from 03 through 08 July 2016. Strokes are color coded by day, and daily totals are in parentheses. Taiwan is in the upper left portion of the map, and the Philippines are to the southwest.
FIGURE 2. Satellite image of supertyphoon Nepartak at 1200 UTC on 06 July 2016.