It's possible that the @NOAA_HurrHunter aircraft just measured the first solid evidence of vertical shear directly attacking the eyewall of Hurricane #Isaias. The last penetration measured an anomalous temperature spike at 750mb within the SW eyewall -—not within the eye—7C higher than the previously measured eye maximum. This might be evidence of a rapidly descending flow belt caused by shear laterally forcing external air into the eyewall region, leading to a massive subsidence inversion. This is often observed in high-resolution modeling (see HAFS sounding from this morning's 06Z run). The dewpoint also sharply decreased concurrent with the temperature spike measured by aircraft, supporting the possibility that this phenomenon was observed. This could foretell significant erosion of the southern eyewall in the near future, but time will tell. For now, Isaias remains as strong as ever according to the same aircraft data.