Halong originated from a broad area of disorganized showers, which simply acted as a source for vorticity which then consolidated into an invest. It was not associated with any typical source for a tropical cyclone.

This system would slowly drift westward over the next few days in-between two areas of ridging, intensifying all the while, and increasing in convective coverage; a fairly rare way for a TC to form, as tropical waves, ITCZ breakdowns and gyres are much more common in the WPAC this time of year.

Models initially expected Halong to continue on a westward track and end up somewhere in-between Japan and mainland China, however as the trough expected to slingshot it northeast became stronger in models, a rapid eastward shift occurred.

Another cause for the fast recurve was the ridge forecast to push it northward becoming weaker, leading to a recurve farther south. All in all, a good outcome, as a C4-C5 storm in the Japan-Korea-China region would likely have devastating consequences.

The organization trend would continue, and eventually the disturbance became a named storm Halong early on the 5th of October. At this time, the vortex was halfway exposed due to northwesterly shear, leaving the LLC spinning in the open while convective activity was concentrated to the southeast.

Halong of the morning and Halong of the night are entirely different beasts - by the evening, shear relaxed somewhat, allowing for the system to become more stacked and begin wrapping convection, especially so after two large bursts quickly curled up shear, beginning the formation of a proper CDO.

The storm quickly intensified to near typhoon strength by the time midnight rolled around, as bands began wrapping around a quickly building core.

On the 6th of October, Halong began intensifying at a more steady pace, firing CBs which would swiftly rotate around the center of the storm. This trend would end up leading to the system being designated a typhoon on the morning of the sixth.

The storm would begin to form an eye early during the day, however a dry air intrusion caused intensification to slow down for the time being. This would last for a mere 12 hours or so, before rapid intensification ensued.

Around this time, the IMS’s TRC (typhoon research centre) announced that as part of project Moonshot, reconnaissance aircraft would sample the storm on the 7th and 8th of October, coinciding with Halong’s peak intensity.

By the evening, Halong was in the process of rapidly intensifying. Due to the aforementioned dry air intrusion, the eye had an easier time forming, as VHTs wrapped around the area of subsidence caused by the dry air, letting the eye develop faster than in a typical subsidence-in-the-CDO fashion.

A microwave pass late on the 6th revealed a nearly closed eyewall underneath Halong’s expansive convective cover, once again indicating that a major typhoon was brewing.

As Halong was intensifying, a very interesting visual phenomena occurred in the northern part of the typhoon. The CDO’s edge became extremely sharp and gradiented, which would usually indicate northerly shear, however in this case it was upper level winds pushing the outflow into a more concentrated channel, rather than fanning out in a slow fashion.

Early on the 7th Halong was approaching peak intensity. The typhoon had began swiftly curving VHTs around a medium-sized eye, as the CDO cooled and stabilized.

Microwave imagery also portrayed an incredible internal structure - a thick eyewall around a medium sized eye. Sadly, we only got a partial pass.

Halong continued improving well into the evening of the 7th, attaining peak intensity around 20z. The storm was likely around 130-135 knots sustained at this time, however due to faulty ADT analysis by SATCON providers, the official peak was kept slightly lower.

Sadly though, as the storm was nearing its peak, a new microwave image revealed that under Halong’s broad CDO, an EWRC prone structure was brewing.

Early on the 8th however, an EWRC brewing since the last evening began taking place, and Halong entered a period of weakening. During this time the system expanded in size while its eye deteriorated, during which a peculiar dry air intrusion lead to Halong possessing “dual eyes”. Of course, this was just a lucky coincidence, as dual eyes are not physically possible, but worth mentioning for how interesting it looked.

Halong managed to complete its EWRC on the morning of the 9th, and put on quite the show - the eye was large and symmetric, with cold cloud tops surrounding it. The CDO was more expansive to the north east, as westerly shear was beginning to encroach on the system’s core.

Microwave imagery of Halong at this time was also extremely noteworthy, showcasing a thick ring around the center of the vortex, at that point looking the most impressive throughout its lifecycle.

After its second peak following the EWRC, the storm entered an environment of 25-30kts of wind shear, which quickly swung it to the E-NE. The typhoon underwent a quick extratropical transition into a strong extratropical cyclone that ended up attaining hurricane force winds.

This system would end up impacting far western Alaska, bringing severe damage, especially coupled with a lack of response from the Trump administration. We hope for a quick recovery to the areas impacted!