The Eyewall of Category 1 Hurricane Paine near Landfall

On October 1st 1986 we used the two NOAA WP-3D's to conduct an experiment in Paine, an eastern Pacific hurricane. During the experiment, Paine had a minimum sea level pressure of ~980 mb and maximum winds of ~40 m/s. It moved north-northeast and skirted the southernmost section of Baja California--a mountainous peninsula with peaks reaching over 1000 m. The two aircraft completed 24 passes from 270 to 1500 m altitude over a 6 hour period focusing on the western eyewall. The lower fuselage radar reveals a distortion in the shape of the eyewall as the storm nears the Baja Peninsula. Our research focuses on the structure and evolution of the eyewall of Paine and its potential interaction with the terrain.

So far, our study has determined several characteristics of Paine. Tangential wind profiles reveal that there is a poorly defined radius of maximum wind (RMW) and weak radial inflows in the lower cloud and subcloud layers. Much of the reflectivity features in Paine appear to be stratiform with tops less than 8 km. However, one striking characteristic of Paine is a persistent reflectivity feature located within the inner eyewall. This feature is 15x15 km, has tops to 16 km, and can be tracked for at least 1.5 hours as it traveled over half way around the circulation center. It is correlated with an inward shift of 8-10 km of the RMW while at the same time showing no increase in the tangential winds. Potential temperature data show that there is little evidence of cool dry air at the surface associated with this feature.

We plan to provide a detailed analysis of the lower cloud and subcloud layers in the western eyewall with in-situ aircraft data. We will use Doppler radar data to derive flow fields near Baja and in the persistent feature. NCEP reanalysis fields are used to determine the synoptic conditions. Finally, we will compare our diagnosed eyewall structure with those derived from more intense hurricanes (e.g. Gilbert, Allen) and with studies of hurricanes near landfall.