Hurricane Polo Makes Landfall in Baja California

Hurricane Polo, at one time an extremely powerful Category 5 hurricane in the East Pacific Ocean and the 2nd most intense hurricane on record in terms of central pressure in the Pacific (storms west of the International Date Line are known as typhoons), made landfall overnight in the central Baja California Peninsula as a Category 2 hurricane just south of Las Barrancas at 11:00 pm MST (6:00 UTC 29 September) with maximum sustained winds reported at 110 mph by the National Hurricane Center (NHC).



Polo originated from a monsoon trough, a broad area of low pressure that typically stretches westward from Central America out into the East Pacific Ocean south of Mexico this time of year and aids in tropical cyclone development. The initial disturbance was also likely aided by a passing easterly wave that propagated westward from the Caribbean over Central America and out over the eastern Pacific. This initial tropical disturbance eventually consolidated and was designated a tropical depression (TD 17-E) by the National Hurricane Center (NHC) at 21:00 UTC on the 20th of September. Located about 285 miles (460 km) south of Manzanillo, Mexico, TD 17-E was quickly upgraded to Tropical Storm Polo at 3:00 UTC on the 21st (9:00 pm CST September 20th) and began tracking back to the east.



Being located over extremely warm waters of ~30 to 31o C (~86 to 87.8o F) due in large part to the emergence of a strong El Niño, which combined with low vertical wind shear, placed Polo in a very favorable environment for intensification. Polo did indeed respond by quickly intensifying into a hurricane just 15 hours later at 18:00 UTC (12:00 pm) on the 21st. NHC reported that Polo underwent an early eyewall replacement cycle and was primed for rapid intensification, which is exactly what happened. Starting at 18:00 UTC on the 21st, Polo’s central pressure dropped from 977 mb all the way down to 892 mb, the 2nd lowest ever recorded for a Pacific hurricane only behind Hurricane Patricia’s 872 mb in 2015, by 19:00 UTC (1:00 pm CST) on the 22nd. In that same period of time, NHC reported that Polo’s maximum sustained winds increased from 80 mph to 180 mph, one of the fastest intensifying hurricanes on record. At this point, Polo was a powerful Category 5 hurricane centered about 360 miles (575 km) south of Manzanillo and nearly stationary.



Incredibly, over the next 4 to 5 days Polo’s intensity oscillated between Category 5 and Category 4, regaining Category 5 intensity twice, as the storm took on a generally west-northwest track well offshore and parallel to the southwest coast of Mexico. Finally, at 3:00 UTC on the 27th (8:00 pm MST on the 26th), Polo dropped to Category 3 intensity with sustained winds reported at 120 mph by NHC as the storm was beginning to recurve to the northwest. At this point, Polo was located about 325 miles (520 km) southwest of the southern tip of the Baja peninsula. Polo then remained at Category 3 intensity over the next 2 days as it continued to recurve first to the north and then the northeast and approach the southwest coast of Baja California on the 28th.



The above animation starts with a time evolution of surface rainfall estimates from NASA’s IMERG precipitation product over the East Pacific Ocean and surrounding region in association with Hurricane Polo. The animation begins at 3:00 UTC on September 20th, before the formation of TD 17-E, and ends at 5:35 UTC September 27th when Polo was paralleling the southwest coast of Mexico. IMERG shows how Polo consolidated into a compact storm with heavy rain concentrated near the center, followed by the development of well-defined banding structures and a central eye indicative of a mature, intense hurricane. The animation also captures Hurricane Odalys, which reached Category 4 intensity, over the Pacific Ocean west of Hurricane Polo.



The 2nd part of the animation provides an inside look into the structure and intensity of precipitation within Hurricane Polo from the GPM Core Observatory when it overflew the storm around 5:35 UTC September 27th (10:35 pm MST September 26th) when Polo was centered about 310 miles (500 km) southwest of Cabo San Lucas, Mexico. Surface rainfall estimates from the GPM Microwave Imager (GMI) show most of the heavy rain (red areas) and banding in the southern half of the storm with intense (magenta) rain wrapping close around the southern half of the center in association with the eyewall.



The actively-scanning DPR can also provide a detailed 3D perspective of the precipitation structure within Polo. Areas shaded in blue denote frozen precipitation aloft, which is mainly in the form of snow, but in the cores of active thunderstorms, graupel (rimed snow particles) and frozen drops are also present. The DPR shows a partial ring of higher tops surrounding the southern half of the center. These deep towers indicate robust thunderstorm activity in the southern eyewall, which is producing the intense surface rain there. This intense thunderstorm activity is releasing large amounts of heat into the core of the storm, sustaining its circulation, and can be a sign of future strengthening. However, the DPR also shows the northern eyewall is relatively lacking. This asymmetric structure suggests Polo has either ingested some dry air or experiencing some windshear, which would inhibit intensification. At the time of the GPM overpass, Polo was a Category 3 hurricane with sustained winds reported at 120 mph. Polo largely maintained this same intensity over the next 2 days as it approached the Baja Peninsula before then weakening to a Category 2 storm at landfall.