Target Sector (2.5-minute interval) JMA Himawari-9 AHI Clean Infrared Window (10.4 µm) images (above) and Red Visible (0.64 µm) mages (below) showed Tropical Storm Bolaven as it intensified to become a Category 1 Typhoon just southeast of the Mariana Islands at 0000 UTC (SATCON | JTWC advisory) on 10 October 2023. The coldest cloud-top infrared brightness temperatures, associated with brief vortical hot towers within the Central Dense Overcast of Bolaven, were around -90ºC (yellow pixels embedded within dark purple areas).

One of the more notable vortical hot towers (VHTs) occurred just southeast of the island of Rota at 0322 UTC on 10 October, as seen in a toggle between Himawari-9 Red Visible (0.64 µm) and Clean Infrared Window (10.4 µm) images (above). The coldest infrared brightness temperature within the VHT cluster of yellow pixels was -94ºC; that temperature represented a significant air parcel overshoot of the local tropopause — which was -81.9ºC at 106 hPa, as seen in a plot of 0000 UTC rawinsonde data from Guam (below). On a side note, the Total Precipitable Water (PW) value of 2.74 in analyzed from that sounding was a record high value for 0000 UTC soundings on 10 October (the previous record was 2.61 in).

Himawari-9 Infrared Window (11.2 µm) images from the CIMSS Tropical Cyclones site (below) showed that Bolaven was moving through an environment of low deep-layer wind shear — which, in addition to its motion across warm water (SST | OHC), favored continued intensification.

View only this post Read Less

Former Hurricane Philippe lost tropical characteristics at 1500 UTC on 6 October, as it interacted with extratopical features moving over it from the USA. (Click here for a UW-Madison weather watch on this event with commentary by Profs Jon Martin and Michael Morgan). There are several players of note in this animation: Philippe, a disorganized mass of convection off the east coast of the US, a subtropical jetstream moving through the southern United States and a potent upper-tropospheric impulse moving from Canada into the upper Great Lakes. Each of these systems have potential vorticity anomalies (different shades of orange in the RGB) that can be tracked.

Philippe’s extratropical transition is coincident with the arrival of a PV anomaly associated with the subtropical jet; that anomaly is moving through the mid-Atlantic states late in the day 6 October/early 7 October. Starting on 8 October, the PV anomaly with the system moving through the Great Lakes also affects the poleward-moving remains of Philippe.

The resultant occluded cyclone remained over eastern Canada through 11 October — as seen below in an animation of surface analyses from the Ocean Prediction Center.

View only this post Read Less

5-minute GOES-16 (GOES-East) Day Cloud Phase Distinction RGB images with overlays of GLM Flash Extent Density, LightningCast Probability and Buoy/METAR reports (above) showed glaciating (brighter shades of green) and glaciated (pale shades of yellow) cloud bands streaming eastward and southeastward off Lake Ontario and Lake Erie on 08 October 2023. Some of these cloud bands were producing lake effect rainfall across parts of western New York and northwestern Pennsylvania.

The 2-km resolution GOES-16 CLAVR-x Cloud Top Height derived product (below) indicated that the maximum cloud top height of these lake effect rain bands was generally in the 25000-30000 ft range (lighter shade of green).

In addition to the rainfall, there were a few areas of GLM-detected lightning associated with these lake effect cloud bands: at 1826 UTC, 1831 UTC and 1951 UTC. LightningCast Probability values had been fairly high at times for several of these lake effect cloud bands throughout the day (particularly the dominant cloud band moving inland from far eastern Lake Ontario) — and had reached 55-75% about 30-50 minutes prior to the majority of the GLM observations of lightning.

Similar to another case, this particular event demonstrated that the LightningCast model does possess some skill in predicting lightning during the cool season.

View only this post Read Less

Tropical Storm Bolaven formed southeast of the Mariana Islands at 1200 UTC on 07 October 2023 (about 540 miles southeast of Guam, according to the initial advisory issued by JTWC). With sufficient illumination from the Moon (which was in the Waning Crescent phase, at 41% of Full), a nighttime Suomi-NPP VIIRS Day/Night Band (0.7 µm) image valid at 1625 UTC (above) showed Bolaven as it was centered about 200 miles northeast of Chukk International Airport (METAR identifier PTKK) on Weno Island.

JMA Himawari-9 AHI Infrared Window (11.2 µm) images from the CIMSS Tropical Cyclones site (below) showed that Bolaven was moving through an environment of low to moderate deep-layer wind shear — and deep convection was beginning to increase south of the storm center.

A Himawari-9 Infrared / Water Vapor Difference product (reference) (below) highlighted areas of deep convection where overshooting tops were likely penetrating the local tropopause (yellow to red to violet enhancement).

Bolaven was also traversing very warm warm water, where Sea Surface Temperature and Ocean Heat Content values were rather high (below).

View only this post Read Less