Tropical Storm 19W (Nineteen)
Tropical Storm 19W has rapidly consolidated over the past 12 hours. Ship reports from the iron yandi (VNVR) over the past 12 hours indicate surface winds from 20-30 knots and slp as low as 1005 mb. VNVR is currently 100 nm north of the center with 110/27 and 1009.2 mb. Upper air data from yap indicated a strengthening low-level circulation center (LLCC) with gradient winds of 30-35 knots at 23/12z.
The system is currently tracking away from yap and the 24/00z upper air gradient winds have decreased to 15-20 knots. The system was upgraded to ts strength based on rapid improvement in organization with curved convective banding, Dvorak estimates also increased and now range from 30 to 45 knots but hesitant to bring system intensity much higher than 35 knots without supporting evidence at this time.
The available model guidance is limited but surprisingly is in good agreement through tau 120. Tropical Storm 19W is tracking under the steering influence of the low-to mid-level subtropical ridge (STR), which is positioned east of the system and is oriented towar the northwest. The 24/00z PGUM sounding showed southeasterly flow at 10-20 knots (700-500 mb). Animated water vapor imagery depicts a developing anticyclone over the center with enhanced poleward outflow due to an upper-low north of the system.
The current position is based heavily on a 232130z SSMI image which shows a defined LLCC with convective banding wrapping into a center near 11.7n 138.5e. There is some uncertainty in this position with satellite position fixes scattered and generally south of this position. The current intensity is based on the lower end of dvorak estimates ranging from 35 to 45 knots.
Tropical Storm 19W is forecast to continue tracking northwestward along the western periphery of the STR toward a weakness near Okinawa. The available models are in very good agreement with this forecast through tau 72. The system should intensify at a 15-knot per day rate under favorable conditions.
In the extended period, there is more uncertainty in the forecast track with two possible solutions. First, the system may slow as it approaches the weakness and re-curve east of Shanghai as the 23/12z ecmwf solution proposes (after tau 120). Or, second, the more likely scenario is that the system stair-steps and tracks westward into the Luzon Strait under the steering influence of the STR over eastern China. This forecast favors the second solution based on the lack of a deep, strong midlatitude shortwave trough in the model fields to induce a re-curve.
The current forecast is based on the consensus of models to include the nogaps, jgsm, gfs, and uk met office models.