Tropical Depression 8 Forms; Kai-Tak Strengthens, Targets China
The tropics are pretty busy tonight, as one would expect during the middle of August, as all three major basins have an active tropical cyclone. The newest of these is in the Atlantic in the form of Tropical Depression 8. According to the 5PM EDT advisory from the National Hurricane Center, the first on this disturbance they have been tracking for days, TD 8 has maximum 1 minute sustained winds of 35mph and a minimum central pressure of 1013mb. This is a rather high pressure for a tropical system. The reason for this is that TD 8 is located in a high pressure environment, so a pressure of 1013mb where it is equates to a pressure of more like 1007-1010mb in a normal environment. According to the NHC, TD 8 is located nearly 600 miles ESE of Bermuda, and moving fairly quickly to the north at 18mph.
Forecast for TD 8
TD 8 is currently in an environment of fairly low shear, which is good for intensification. It is also over waters warm enough to allow for intensification. The only inhibiting factor is dry air, as there is a fair amount surrounding the system. While TD 8 is currently surrounded by less dry air than it has been in recent days, its small size will make it vulnerable to the dry air, limiting convective building which will help limit significant intensification. Figure 1 shows that despite its good structure, TD 8 does not currently have very deep convection, indicative of dry air hurting the system.
Figure 1: TD 8 has a solid structure for a depression, but will need more convection to strengthen significantly.
In addition, TD 8 has a fairly short window of opportunity to strengthen as the SHIPS intensity model indicates nearly 50kts of shear will hit the system in about 4 days, which will weaken it as it starts to undergo extratropical transition. Despite some limiting factors, the NHC forecasts strengthening, as they call for a peak intensity of 70mph in about 3 days, which would make TD 8 a strong tropical storm. My intensity forecast is very similar, as I am thinking a peak of about 75mph late Saturday or early Sunday, meaning TD 8 would reach minimal hurricane status.
The official forecast track from the NHC is shown in Figure 2.
Figure 2: Official NHC track forecast for TD 8.
TD 8 should continue a generally northward movement for the next 8-12 hours, followed by a hard northeast and then east turn. Eventually TD 8 should begin moving back towards the northeast as a trough captures it and sends it in the general direction of the Azores in 4 days or so as it begins to weaken and become extratropical. It is a rather odd track but is in line with dynamic model guidance so I am inclined to believe it is correct. If anything a slightly more southerly track is likely in my opinion and I do not believe TD 8 poses a significant threat to the Azores. Nonetheless, tropical storm watches or warnings may be required at some point.
In the East Pacific, Hector has weakened to a tropical depression as of the 5PM EDT advisory from the NHC. Hector's maximum 1 minute sustained winds are estimated at 35mph and its minimum central pressure is estimated to be 1003mb. It is interesting to note that this pressure is 10mb lower than that of TD 8 despite the systems having the same wind speeds. Hector should continue to weaken for the next day or two as it is struggling with significant wind shear and will be moving over cooler waters as it drifts N to NNW well away from land areas. Hector will most likely be dissipated by this time tomorrow.
Figure 3: A weakening Tropical Depression Hector.
Kai-Tak Now a Typhoon
Meanwhile, the active, landfall filled season in the West Pacific is continuing right now due to recently upgraded Typhoon Kai-Tak. According to the latest warning from the Joint Typhoon Warning Center, Kai-Tak has maximum 1 minute sustained winds of 65 kts, or 75 mph, making it a minimal typhoon. It is located about 320 nautical miles SE of Hong Kong and is moving W at about 11kts. Kai-Tak has already dumped torrential rains on the Philippines, and it is now poised to do the same for southern China as the official JTWC track forecast keeps the system on a WNW heading for the remainder of its lifespan.
Figure 4: Official JTWC track forecast of Kai-Tak. It should make landfall in about 36 hours.
JTWC has struggled miserably with the track forecast for Kai-Tak, as not long ago it was forecast to brush southern Taiwan and head into China well north of Hong Kong. Guidance has now come into agreement however, so track forecast confidence is high. It is likely that Kai-Tak will intensify slightly as it nears landfall, probably peaking as a high end category 1 storm though intensification to a category two is not out of the question as we have seen multiple storm rapidly intensify in the West Pacific this year. Regardless, extremely heavy rainfall and dangerous mudslides will be the main threats.
Figure 5: Typhoon Kai-Tak, with its very deep convection, a distinguishing characteristic of many West Pacific storms.
I was working at the Blue Hill Observatory today and wrote much of the daily discussion, which you can read here. We had a decent thunderstorm move through early this morning so some of the observation remarks are pretty interesting. I would check it out.
Thank you as always for reading, and enjoy the rest of your week!