Subtropical Storm Surigae (Philippine name Bising) is located 1056 km west of Iwo To, and has moved east-southeastward at 11 km/h (6 knots) over the past 6 hours.
Infrared imagery shows a broad, exposed low-level circulation with isolated, flaring deep convection confined to the eastern quadrant associated with a shortwave trough propagating northeastward over the northern quadrant of the system.
Visible imagery and a SSMIS color composite image show tightly-curved shallow banding wrapping into a well-defined center supporting the initial position with good confidence.
The initial intensity is hedged slightly above the PGTW subtropical intensity estimate (using the hebert-poteat subtropical method) of st3.0 (45-50 knots) based on recent ASCAT data and the well-organized low-level structure.
Surigae is embedded within the subtropical westerlies under 75-95 km/h (40-50 knots) of westerly wind shear and is tracking over cooler sea surface temperatures (24-25°C) along with significant mid-level dry air entrainment.
Surigae will continue steadily weakening over the next 24 hours as it loses baroclinic support from the upper-level shortwave to the north but is expected to retain gale-force winds.
In around 36 hours, a second shortwave trough currently entering the Yellow Sea will approach Surigae, reintroducing baroclinic forcing. This may strengthen and intensify the wind field slightly by 2 days, and will also bring about the conclusion of extratropical transition.
The forecast track is similar to the previous one, passing near Iwo To in around 36 hours. The model guidance envelope is tightly clustered, with some slight variation in forward speed.
Overall, this forecast is of high confidence.
Current sustained winds: 100 km/h winds
