(BIVN) – Tropical Storm Pena formed suddenly on Friday to the southeast of Hawaiʻi, where an area of low pressure has been developing over the last few days.
As of 11 a.m. on Friday, Pena was located 650 miles southeast of the South Point area of Kaʻū. The storm is moving west at 12 mph, and is forecast to pass well to the south of the Hawaiian Islands. Pena is expected to gradually strengthen over the next day or so.
“This system will likely boost trade wind speeds as it will likely track too far south for any rainfall impacts,” the National Weather Service in Honolulu stated.
From the Central Pacific Hurricane Center discussion posted at 11 a.m. HST:
Satellite imagery indicates that an area of low pressure (Invest CP95) that we have been monitoring for several days has developed a well-defined circulation, showing banded convection around its center. While the most recent constrained subject Dvorak analysis from HFO was CI number was 2.0/30 kt, the Data T was 3.0/45 kt, which probably better reflects the system’s organization. A 1546 UTC SMOS microwave pass supports that assessment, showing winds above tropical-storm-force east of the center. Based on this, advisories have been initiated on Tropical Storm Pena, with an intensity of 40 kt.
The initial motion is estimated to be westward, or 280/10 kt, and the storm is expected to continue this motion for the next several days due to a high pressure ridge centered over the Central Pacific. Model guidance remains in good agreement through 72 h on Pena’s track, then cross-track spread increases among the model solutions, resulting in lower-than-normal confidence. Additionally, the storm’s initial representation in much of the guidance is too weak, which adds another layer of uncertainty. The NHC track forecast has been set to follow the GDMI and HCCA aids.
The intensity forecast is tricky because the overall environment generally seems conducive to strengthening for at least the next day or so. While there is an increase in shear in much of the models this weekend, this shear could abate early next week, with no obvious dry air or instability issues seen in the large-scale guidance. It is a little puzzling why many of the models show little change or even a weakening so quickly in seemingly conducive conditions, though perhaps it is linked to the unrealistically weak initial vortex representation of Pena. The first forecast is on the higher side of the guidance and reflects a blend of some aids that get close to hurricane-strength, while others weaken to a depression. It probably goes without saying that this too is an uncertain prediction, similar to the track forecast.
