Finally-to-be-Typhoon Durian
Good morning.
Two-and-a-half days after this thread was started, Durian will finally complete the slow crawl to typhoon status with the next forecast from JTWC (#12). Overnight, intensity was upgraded from 55 kt to 60 kt as expected, and the most recent satellite intensity estimates are agreed by SAB and JTWC to be T4.0.
In just the last couple of hours, deep convection was finally able to wrap most of the way around the center, under the recently-formed CDO. As recently as 0900Z, microwave imagery showed very spotty convection, but a more recent pass from around 1130Z showed much improvement, and, having gotten past the catch-22, this will provide the protection the core needs to develop. Like trying to start a fire under slightly adverse conditions, Durian's "flames" have finally caught, and we can now expect a modest blaze to begin. And finally the anemic shallow convection of the last couple days has been replaced by colder cloud tops (although still somewhat shallow). The poleward outflow that was mentioned is finally starting to form this morning, concurrent with the development of the core convection, starting around 1000Z; the plume of moisture to the north making inroads into the dry air clearly seen on water vapor imagery.
Last night I understood why typhoons tend to rapid intensification here. The natural positioning of the upper level winds provides tremendous outflow. But to paraphrase Avila from an advisory on Sergio last week, it ain't all about the outflow. The reason development was slow, and was expected to be slow, over the past couple days was due to continued dry air intrusion. Increased outflow means increased inflow, and dry air from the north and west was repeatedly eroding convection.
I wouldn't be overly surprised to see Durian reach 90 kt by this evening (290000Z), although, since there is some evidence that a smaller eye is forming, and the storm has organized rapidly in the last couple of hours, already shedding the spiral bands for a compact core (however, still pulling moisture from the ITCZ -- in fact has pulled a considerable amount of moisture from there overnight, increasing the "boundary" between the core and the drier air, which is probably what enabled it to get going), I wouldn't think it completely out of the question to see Durian reach 100 kt to 105 kt today either.
Update: With forecast #12, JTWC stayed with 65 kt, citing the less-than-impressive Quikscat from 0941Z, which however was timed just at the beginning of the recent organization of the convection. They also mention the developing poleward outflow. They are forecasting 80 kt by 29000Z, and, reviewing recent water vapor imagery, I may have gotten carried away just a smidgen with an estimate of 90 kt. But, in spite of some drier air which has managed to wrap almost completely around the core of the the typhoon, starting from the northwest at around 0900Z, a more recent
microwave pass from around 1300Z shows continued improvement in the small core.
The track forecast is very touch-and-go, and the JTWC discussion was thorough; it appears likely that northern Luzon will be grazed, and that a more direct hit cannot be ruled out. JMA has not diverged from their forecast of a more westward track landfalling in the central portion of the Philippines.
