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!
Tropics Quieting, No Threats on the Horizon
The tropics have significantly calmed over the past couple days. There is now just one active tropical cyclone in the world, Tropical Depression 8E in the East Pacific. As of the 5PM EDT advisory from the National Hurricane Center, 8E is located just over 200 miles WSW of Manzanillo, Mexico, and is moving west at 10mph. Maximum sustained winds of this system are estimated to be 35mph in accordance with satellite estimates. The minimum central pressure of the system is 1001mb. Tropical Depression 8E is actually the remnants of Hurricane Ernesto from the Atlantic. However, because the NHC said that Ernesto's circulation dissipated over Mexico, 8E will be renamed Hector, the next name on the East Pacific list, not Ernesto, if it gains tropical storm strength.
Forecast for 8E
The main inhibiting factor for intensification of 8E is wind shear. According to the latest run of the SHIPS intensity model, shear will remain between about 15 and 25 kts for the next 5 days. Ernesto is in a moist environment and over warm waters, so neither of these critical factors will hinder strengthening of 8E. The NHC is forecasting a peak intensity of 70mph in about three days before cooler waters begin to weaken the system. The intensity forecast is interesting because most intensity model guidance is showing very limited intensification, likely meaning they think the shear will prevent strengthening. However, I think the one thing that will help 8E to hold off the shear is its very large size. Generally, large systems are much more efficient at strengthening in a moderate shear environment than small, fragile ones. Therefore despite no intensity models forecasting this, I think Ernesto, like so many East Pac systems in recent years, will reach hurricane status and peak at around 90mph. This is a very low confidence forecast, however, as it is possible shear will prevent 8E from strengthening much above minimal tropical storm status.
Figure 1: Tropical Depression 8E.
There is also some uncertainty in the track forecast for 8E. The majority of models agree on a general west motion for the next couple days, possibly followed by a brief WSW turn as the NHC official forecast suggests. Several models then show the system bending back towards the NW. A couple of models, most notably the CMC, take 8E on a more northerly track towards Baja California. 8E is being steered by a strengthening ridge, so a general W motion should continue for a few days. However, since I am forecasting a stronger system than the NHC, I think 8E will weaken this ridge more than forecast and allow for a track a bit farther north than the official NHC forecast. I still do not anticipate 8E being a threat to land areas as cooler waters should weaken the system before it gets close to Baja California, if it goes that way.
Figure 2: Official NHC forecast track of 8E.
Also in the East Pacific, former Hurricane Gilma weakened to a remnant low today, as the NHC issued its last advisory on the system at 5PM EDT. Like so many East Pacific systems, it weakened due to cool sea surface temperatures and is now just a convectionless swirl.
Figure 3: The remnants of Gilma.
TD 7 Dissipates
In the Atlantic basin, Tropical Depression 7 dissipated today after a hurricane hunter mission this morning failed to find a closed circulation. This dissipation comes as little surprise as former TD 7 was in an area of unfavorable conditions and was never expected to strengthen much. As of their 2 PM Tropical Weather Outlook, the NHC is giving the remnants of TD 7 a 10% chance of redeveloping in the next 48 hours. I do not see any redevelopment of this system as it tracks through the Caribbean.
Figure 4: The remnants of TD 7, now an open wave.
93L Struggling, May Develop Later
In the far Eastern Atlantic, Invest 93L is struggling in the face of cool waters and dry air. As of the 2PM TWO, the NHC is giving 93L just a 10% chance of developing in the next 48 hours, a percentage I agree with. I still believe that development of this system is possible at some point in the next week as it moves into conditions that are a bit more conducive for development. If 93L were to develop, it should head out to sea without threatening any land areas.
Looking long range, the GFS continues to show development of multiple systems off Africa, but it has been very inconsistent lately so I do not anticipate much development in the next 1-2 weeks, and anything that does form should head out to sea.
Figure 5: The end of today's 12z GFS run, showing multiple systems. The model continues to indicate my prediction of a predominantly recurve pattern this month is on track.
Thank you for reading. Enjoy the rest of your weekend!
Several Interesting Areas, But No Major Threats
As would be expected as we close in on mid August, the tropics are quite active tonight. In the Atlantic there are two areas being watched right now. The first is Tropical Depression 7. According to the latest advisory from the National Hurricane Center, Tropical Depression 7 is located just over 500 miles east of Barbados, and is racing west at 23 mph. TD 7 currently has maximum sustained winds of 35mph, and a minimum central pressure of 1009mb.
Forecast for TD 7
Tropical Depression 7 has two main factors working against it. The first is a very fast forward motion. It is very difficult for small, weak systems like this to organize when they are moving at over 20mph like TD 7 is. Another problem is dry air, as Figure 1 shows.
Figure 1: Water vapor image of TD 7.
While TD 7 has done a fairly good job at not letting the dry air disrupt its circulation, the dry, stable air is still preventing it from firing up a significant amount of convection. Shear, meanwhile, is moderate, as the SHIPS model indicates TD 7 will be going through 10-15 kts of shear for the next 36 hours or so but 15-25 kts after that. The National Hurricane Center forecasts little strengthening of TD 7 as they indicate a peak of only 40mph before dissipation in 3 days. I think the marginally favorable present shear conditions, combined with DMAX tonight, will give TD 7 enough of a boost for it to be named Gordon tomorrow morning, possibly at the 5 AM advisory. After that, however, I, like the NHC, see the system dissipating due to unfavorable conditions. A recon mission is scheduled to investigate the system tomorrow morning, and it wouldn't be shocking if they found TD 7 an open wave. The track forecast is a little tricky as it depends on intensity. A stronger TD 7 would be more likely to get pulled further north and track through the northern Caribbean. However, a weak one, like myself and the NHC forecast, is more likely to go south. Therefore, I think a track similar to that of the NHC, seen in Figure 2, or perhaps one slightly farther north, is likely.
Figure 2: Official NHC forecast track of TD 7.
Invest 93L Struggling
The other area being watched in the Atlantic is Invest 93L. 93L is located in the far Eastern Atlantic, near the Cape Verde islands. After looking good last night and into this morning, I was really buying that 93L would develop by tonight. However, drier air and cooler waters have prevented this as the NHC now gives this system only a 30% development chance in the next 48 hours as of their 2PM Tropical Weather Outlook. I still believe this system will eventually develop, and I'm not entirely ready to give up on the idea of this becoming a formidable storm eventually. After it passes the Cape Verde islands, 93L should be no threat to land for several days, so there is plenty of time to watch this situation unfold. Should it develop, a recurve definitely looks like the most likely scenario, as I continue to believe that will be the theme for this month.
Ernesto Attempting His Comeback
After dissipating over Mexico earlier today, Tropical Storm Ernesto is now emerging into the waters of the East Pacific. Since he was declared dissipated he is now Invest 94E. As of their 2PM TWO, the NHC is giving 94E a 70% chance of development in the next 48 hours. I put these odds higher, closer to 90%, since 94E already looks like a tropical cyclone. 94E is providing heavy rains to Mexico, but after it pulls away from the coast it should not be a threat to any land areas.
Figure 3: Invest 94E
Also in the East Pacific, former Hurricane Gilma has weakened to a tropical storm. Moving over cooler waters, Gilma should continue to weaken and poses no threat to any land areas.
Figure 4: Tropical Storm Gilma
I've posted a couple of these links on the blog, but if you've missed them these are the four most recent daily discussions I've helped to prepare with the Blue Hill Observatory:
Thank you for reading, and have a great night!
Tropical Weather Outlook
We're definitely to that time of year now. Hurricane season is nearing its peak, and after a quiet July we have already seen two storms one week into August. There are three main features tonight. The first of those is Tropical Storm Ernesto. Ernesto spent most of its life failing to live up to expectations, but that all changed yesterday as Ernesto strengthened significantly from a moderate tropical storm to nearly a Cat 2 hurricane prior to landfall on the Yucatan Peninsula. Ernesto is now emerging into the Bay of Campeche. It weakened quite a bit over land as would be expected, but it retained a solid overall structure so it should strengthen some in its short time over the BOC. Its current maximum sustained winds are 50mph as of the National Hurricane Center's 8PM EDT intermediate advisory. It is moving W at 7 mph, and this general motion with a bend more to the WSW should continue until dissipation over Mexico on Friday. As Figure 1 shows, Ernesto will not be over water long, so I don't see a second peak any higher than 65mph.
Figure 1: Visible loop of Ernesto, showing how it is now emerging over water once more.
The second feature being watched is Invest 92L. 92L is currently located about 950 miles W of the southern Cape Verde islands according to the National Hurricane Center. The NHC is giving it a 50% chance of development in the next 48 hours. 92L's window of opportunity is short, as SHIPS indicates wind shear will increase to 20 or more knots beyond 48 hours. Even now conditions are not ideal as there is a good deal of dry air in front of the system. Nonetheless, organization has improved today, so some development is possible. I think's its pretty much a coin flip on whether it happens or not, so I'll play it safe and side with the NHC and give 92L a 50% chance of development in the next 48 hours.
Figure 2: Invest 92L. Deep convection is less than impressive, but structure is improving.
The third and final area of interest tonight is a vigorous tropical wave over Africa that will be emerging over the far eastern Atlantic in less than 2 days. There are more questions than answers with this system. The most aggressive model for development has been the GFS, with the ECMWF also showing some development. There have been a lot of inconsistencies however, especially in the GFS. Runs from a couple days ago were fairly consistent in showing this wave becoming a powerful hurricane and threatening the East Coast. Recent runs have been much more inconsistent, with the last 4 runs showing a Southeast storm, a Northeast storm, an out to sea storm, and nothing at all on the most recent run. Based on what a powerful wave this is I do think we will see development, and I still believe there is a good chance this system will end up being a Cape Verde hurricane. However, I think the most likely scenario for this storm is a recurve out to sea. I consider myself pretty good at reading between the lines on the models. The 6z GFS showed a big storm for the Northeast, but by the end of the run the dominant high pressure system had backed way off to the east. The generally more reliable 12z run painted a very accurate potential scenario in my opinion as it backed the high up enough to allow for a recurve with room to spare for the US. 18z tonight was not at all accurate with intensity in my opinion but once again had the idea of moving the high back. In addition, the GFS ensemble means and individual members have been showing the high moving back. So while the GFS has shown a lot of landfalling or nearly landfalling systems, I think it will begin to become more consistent in showing a recurve. The ECMWF did not pick up on development as fast as the GFS, but it has now and it is also showing the high getting pushed way back, maybe even a little too far, allowing for storms to recurve very early on. The UKMET and NOGAPS have also shown signs of the high weakening and/or pushing back. Making predictions for so far out is risky, but I have higher than normal confidence for a long range forecast that the overall pattern this year will favor recurving storms for anything that forms around or before 40W. This means that the biggest threat for US landfalls will come from storms forming in or close to the Caribbean and in the Gulf of Mexcio. Of course, the models could flip back and end up keeping the high where it is or the high could weaken and move back briefly before building back in, but I just don't see that right now. While I;m on the subject of long range predictions, I think my forecast of 12 named storms this year is pretty much on track, or it may be just slightly too low. I think we could easily see Gordon, Helene, and Issac in the rest of this month, then Joyce, Keith, and Leslie in September, and one or two more storms in September or October. It definitely looks like our biggest threat will be from home grown systems.
Thank you as always for reading. I'd love to hear your thoughts on what you think the year's dominant pattern will end up being. Enjoy the rest of your week!
Tropical Weather Outlook for the Weekend
I just wanted to give a very quick update on my thoughts for our three areas of interest in the Atlantic. I am heading to Cape Cod this weekend to swim with the sharks so I won't be on again until Monday morning. These are just my predictions for the next 2 days.
Definitely the biggest threat in the Atlantic right now, I think Ernesto should continue to steadily organize through the weekend. It has looked better all day after nearly dissipating last night, so I think a continued strengthening is likely. I am thinking a track similar to that of the NHC at least in the short term. As for intensity, rapid strengthening over the next 2 days is unlikely since conditions won't be overly favorable for intensification, with some wind shear and some dry air. Nonetheless, I would not be surprised to find a Cat 1 hurricane when I return home.
11 PM tonight: 60mph
5AM Saturday: 60mph
11PM Saturday: 65mph
5AM Sunday: 70mph
11PM Sunday: 75 mph
Beyond this, I am thinking Ernesto will come close to the northern Yucatan, possibly heading through the Yucatan Channel. My forecast for a Texas landfall hasn't changed. A weak Ernesto would likely head for Central America/Mexico, while a strong one (Cat 3 or more) would likely head more towards LA or the FL panhandle. I think something in between is likely, with Ernesto peaking as a Cat 2 and heading for north Texas.
Figure 1: Tropical Storm Ernesto.
Figure 2: Official NHC track forecast. I'm thinking a similar track to this short term with a slightly more northerly track long term as Ernesto intensifies to Category 2 status.
Located in the far east Atlantic, invest 90L formed from a vigorous tropical wave today and has been looking better and better all day. The NHC gives it a 50% chance of development in the next 48 hours. As long as 90L maintains its current satellite appearance, it should be declared a TD tonight or tomorrow morning, so I put the odds at a higher 80%. Conditions are fairly favorable for development, so some strengthening is likely It certainly won't be a threat to land in the couple days I will be gone so I won't go into much detail here. My early thinking is that it won't head for the US, but Bermuda may need to watch this one.
Our newest invest, 91L, is located near the Bahamas and SE Florida. It has been looking better since being declared and the NHC gives it a 20% chance of development in the next 48 hours. I put these odds closer to 40%, but I don't foresee 91L becoming a named tropical system. Regardless, the impacts will be the same for Florida: Heavy rains and gusty winds. 90L should keep moving NW into Florida. Shear is currently very high off the west coast of Florida, so unless this changes I don't see development of 91L over the Gulf either.
Figure 3: Invest 91L.
Elsewhere, the East Pac is very quiet. In the West Pac, newly named Tropical Depression Haikui has the potential to be a significant threat to Japan in a week or so. I will talk more about this when I get home.
Thank you very much for reading. Have a great weekend!!!
Updated: 9:36 PM GMT on August 03, 2012
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