The Role of Observed Environmental Conditions and Precipitation Evolution in the Rapid Intensification of Hurricane Earl (2010)

Abstract

An investigation into the possible causes of the rapid intensification (RI) of Hurricane Earl (2010) is carried out using a combination of global analyses, aircraft Doppler radar data, and observations from passive microwave satellites and a long-range lightning network. Results point to an important series of events leading to, and just after, the onset of RI, all of which occur despite moderate (7-12 m s 21 ) vertical wind shear present. Beginning with an initially vertically misaligned vortex, observations indicate that asymmetric deep convection, initially left of shear but not distinctly up-or downshear, rotates into more decisively upshear regions. Following this convective rotation, the vortex becomes aligned and precipitation symmetry increases. The potential contributions to intensification from each of these structural changes are discussed.The radial distribution of intense convection relative to the radius of maximum wind (RMW; determined from Doppler wind retrievals) is estimated from microwave and lightning data. Results indicate that intense convection is preferentially located within the upper-level (8 km) RMW during RI, lending further support to the notion that intense convection within the RMW promotes tropical cyclone intensification. The distribution relative to the low-level RMW is more ambiguous, with intense convection preferentially located just outside of the low-level RMW at times when the upper-level RMW is much greater than the low-level RMW.

Climatology of overshootings in tropical cyclones and their roles in tropical cyclone intensity changes using TRMM data

“…However, this is inconsistent with previous observational case studies (e.g., Reasor et al 2009;Guimond et al 2010;Molinari and Vollaro 2010;Nguyen and Molinari 2012;Reasor and Eastin 2012;Stevenson et al 2014;Rogers et al 2015;Susca-Lopata et al 2015), which emphasized the role of asymmetric very deep convection in RI. As mentioned in section 3.7, most of these observational case studies are biased toward the ending period of RI, while the three studies about Hurricane Earl (2010) focused on deep convection before RI while the storm was in the slowly intensifying stage.…”

“…A vortical hot tower was observed 7 h before the RI event of Tropical Storm Gabrielle (2001) ended (Molinari and Vollaro 2010). There are several recent studies about Hurricane Earl (2010) (Stevenson et al 2014;Rogers et al 2015;Susca-Lopata et al 2015) showing asymmetric deep convection around 6-9h be-fore the onset of RI (Fig. 3.13).…”

“…At this time, isolated very deep convection is often observed ( Fig. 3.3c; Stevenson et al 2014;Rogers et al 2015;Susca-Lopata et al 2015), which is possibly due to high wind shear ( axisymmetrization (Kieper and Jiang 2012;Susca-Lopata et al 2015), and more latent heat release. As RI continues, increased moderate to very deep precipitation is observed, producing much higher total volumetric rain and latent heating release (Figs.…”

“…The convective evolution in RI storms is examined extensively in recent case studies (e.g., Stevenson et al 2014, Susca-Lopata et al 2015. Stevenson et al (2014) The dataset for this study is derived from the TRMM Tropical Cyclone Precipitation Feature (TCPF) database (Jiang et al 2011), which includes the overpasses of all global TCs viewed by the TRMM satellite.…”

“…While these satellite-based statistical studies implied that the symmetry of widespread precipitation containing a much lower percentage of asymmetric deep convection is important in initiating RI in the following 24 h, observational case studies mentioned above (Reasor et al 2009;Guimond et al 2010;Molinari and Vollaro 2010;Nguyen and Molinari 2012;Reasor and Eastin 2012;Stevenson et al 2014;Rogers et al 2015) emphasized the role of asymmetric very deep convection in RI. An important question raised from this is, what is the relative importance of precipitation-convection of different depths-intensities to RI?…”