Windspeed
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Everything posted by Windspeed
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If ever there was a case in point, this is it. 5+ days out you might peek at the operationals for patterns, precip, derived winds, feature locations, and especially entertainment purposes, but for estimates on TCs and their storm relative potential, you go with the different ensemble packages all night and day long. I don't mind beating that dead horse into a smear until frequent posters get it.
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Possible Atlantic MDR development next week being modeled in several ensemble camps.
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Good lord that AEW went poof!
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Well it is a large wave with a noticeable mid-level circulation. It appears to have exited slightly more north and will pass through the Cabo Verdes. It also has a very nice mid-level moisture envelope around it. Obviously there is very stable dry air, but well NW of the wave itself. SSTs at that latitude are marginal but as it keeps gaining longitude, they do increase to support genesis. We'll just have to keep an eye on it. It is color-coded orange by the NHC with 40% probs in the 5-day outlook.
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What the hell is going on with the GFS lately? Sheesh...
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There it is, Chief... Jokes aside, that is the most impressive sub-Saharan MCS I have seen since Irma. This is going to be fun to track regardless of pattern shenanigans. Granted, Florence's was nice too, but not that intense.
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We've been in an unfavorable phase, but favorable upper 200 hPa vorticity is now spreading over the Atlantic Basin and should have a negative mean through the end of August. Afterwards, a rather neutral phase will persist over the western basin with stronger vorticity remaining over the far EATL/WAM. At any rate, you don't need a strong MJO, you just don't want to see a suppressive regime dominating the entire basin. Upper divergence should persist over the WAM through peak season to keep strong AEWs exiting the African continent.
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Mentioning this here as it relates to an overall pattern feature. The MJO is currently increasing favorability across the Atlantic Basin as was forecasted. This should remain in place for the next few weeks, perhaps longer. Interestingly, one of the side effects of robust upper 200 hPa vorticity can be a negative when associated with a monsoonal trough. That's exactly what we have going on in the EATL right now. The WAM extension west into the MDR with two competing wave axii and strong low-level convergence amplified by the ITCZ. This is otherwise generally great for TCG; however, if you have multiple regions of vorticity within close proximity and robust convection occurring over a large area, it can sometimes take an extended period of time for one of the competing regions of vorticity to become dominate. If these regions were further apart, you'd likely get two TCs develop. A favorable MJO phase is always better for TCG than a an unfavorable phase. But there can still be caveats. There has also been research done on how a positive MJO phase influences rapid intensification. Interestingly, it was determined that though the MJO greatly enhances convection to allow for TCG, it doesn't necessarily help with rapid intensification of a particular cyclone. Again, competing convection may have something to do with this as the internal convection within the TC's vortex structure may have to compete with surrounding areas of convection. Sometimes that can be a negative factor, though perhaps not as much if the vortex is already intense. We saw this occur with Major Hurricane Matthew in the deep Caribbean back in 2015. It became a Category 5 despite having to compete with backside intense MCS complexes with competing MLCs rotating outside its main vortex. Though there is a need for more research to be done, I suspect the best scenario for TCG would be an isolated wave convectively influenced by a favorable MJO phase, but not one so strong that it over-amplifies surrounding regions of convection, which may induce subsidence on the resulting TC. Obviously when dealing with a monsoonal trough with multiple wave axii, the possibility of slower tropical development may be a real thing. Though that tends to work itself out when one of the low-level vortices eventually becomes dominate. We'll see how this evolves with 98L. In the meantime, 97L may benefit from the phase much more favorably for TCG in the next 24-36 hrs, as it is certainly isolated, and will position itself in a region of the Caribbean for improved low-level convergence as low-level wind profiles becomes more favorable. Upper divergence isn't an issue. There is some dry air, but the overall upper pattern is favorable.
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2PM EDT Outlook: ZCZC MIATWOAT ALL TTAA00 KNHC DDHHMM Tropical Weather Outlook NWS National Hurricane Center Miami FL 200 PM EDT Mon Aug 17 2020 For the North Atlantic...Caribbean Sea and the Gulf of Mexico: 1. A tropical wave approaching the Windward Islands is producing a large area of disorganized shower and thunderstorm activity. This disturbance is moving westward at about 20 mph, and is expected to continue to move quickly westward over the eastern and central Caribbean Sea during the next couple of days, which is likely to limit significant development. After that time, however, the system is expected to move more slowly westward across the western Caribbean, where upper-level winds could become more conducive for the development of a tropical depression during the latter part of this week. Regardless of development, locally heavy rainfall and gusty winds are expected over portions of the Windward and southern Leeward Islands through Tuesday morning. * Formation chance through 48 hours...low...20 percent. * Formation chance through 5 days...medium...50 percent. 2. A tropical wave over the eastern tropical Atlantic is forecast to interact with another disturbance located several hundred miles southwest of the Cabo Verde Islands within the next day or two. This interaction is expected to lead to the formation of a broad area of low pressure, and conditions are forecast to be conducive for the development of a tropical depression during the middle-to-latter part of this week while the system moves westward to west- northwestward at 15 to 20 mph across the central and western portions of the tropical Atlantic. * Formation chance through 48 hours...low...30 percent. * Formation chance through 5 days...high...70 percent. Forecaster Brown
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You're going to come off as quite bipolar in your postings if you start hanging on each GFS operational run for long-range track and immediately making a declaration of death in your "outlook" of the upcoming period every time that track doesn't pan out. The very next run could have an entirely different TCG location and resulting stronger track intensity ~120 hrs out. Best to just realize we have potential development to follow. The ensembles are still more valuable in the long range as has already been stated multiple times, repeatedly. When we actually do have a TC to track, we then may start focusing more on operational track placement and pattern, though you still must be cautious beyond 144+ hrs for the downstream pattern, as that can easily flip. At any rate, your persistent declarations about the peak season being this or that based on single operational model outputs every six hours is not particularly contributive to the discussion. That's not to say we should not point out a pattern that swings more unfavorable. But that is entirely not what is being suggested by modeling here in the mid-to-long range.
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Thought that was already deemed 98L. Sometimes they'll discuss them as ALxx. Former NHC Specialist Kimberlain referred to the disturbance as AL98 earlier. At any rate, unsurprisingly the GFS weaker in the mid-to-long range with the potential TC due to tracking through the Greater Antilles and timing/position being not as aligned with strong upper ridging. That upper ridging is a beast though and is probably more the takeaway; i.e., IF a TC gets positioned under that, things could escalate quickly.
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Nice post by Todd Kimberlain. My takeaway here would be AL98 staying relatively weak regardless of TCG until it begins to approach the Lesser Antilles. Lower steering flow will begin to align more with upper steering flow, which would likely allow the system to stack better vertically. The GFS has been a little wonky with convective feedback over the EPAC in the long-range, given some of the oddball convective spin-ups after Genevieve considering the shift of upper 200 hPa vorticity eastward; yet it continues to show a mighty large upper ridge / anticyclone developing over the Caribbean and GOM late in the period, which could spell trouble if a hypothetical TC is moving through the region. There is also a strong STJ that splits flow and ejects eastward over the Southern CONUS. That would seemingly decrease upper level westerlies over the NW Caribbean and GOM downstream. Again, this all means squat if there is no TC there to take advantage. I am still apprehensive of the GFS right now. So take the strong fantasy Caribbean runner with a grain of salt until we actually have a TC to track.
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In the short-term, the wave just east of the Lesser Antilles does have weak vorticity and increasing convection, especially on its SW axis. Some of last night's EPS showed potential development of this disturbance, though today's 12z ECMWF operational keeps this open into central America. The 12z UKMET and GEM operationals are much more forgiving and do want to produce a TC as it traverses the deep Caribbean. No need to mention the 12z GFS since @Idub23 has that covered into September. [emoji6]
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12z ECMWF now runs a TC, presumably the AEW that just exited Africa, just north of the Antilles through the Florida Straits and deep into the Gulf. Extends WAR and builds heights. Obviously this is way out in fantasy long range, but we now have a major operational model coming into line with its ensembles. Was only a matter of time. Now we'll just have to be patient and see how TCG occurs and where. Additionally how the upper pattern will unfold as any potential systems reach the WATL. We are too far out to know if any particular potential TC will aligned under a favorable or unfavorable setup. A lot of variables and a lot depends on downstream TUTT evolution, split and where those upper heights build specifically. Overall takeaways should just be increased potential for a long-tracking TC out of the MDR and notable WAR extension.
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Long range European ensemble continues up...
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Andy commenting on the EPS and Caribbean potential in the ~200 hr range. Note the powerful upper ridge being modeled over the Caribbean. Granted, the operationals do not have a TC under this feature yet. They may of course never. However, the EPS ensembles do and also have that upper ridge. Depending on TC placement, of course, that would support a powerful TC from the S. Bahamas to the NW Caribbean barring land interaction. Obviously this doesn't mean Jack Squat if there's no TC. But that's why you watch the ensemble packages for potential vorticity. At any rate, with MJO coming aboard in that range, this is all we've got until the ops do eventually start getting into closer range to better resolve something and we can see how those runs will start panning out.
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You don't really focus on strength, you focus on signatures. That there are numerous possible tropical lows means potential increases for something to be somewhere favorable or unfavorable. At ~200 hrs all your looking for are potential low placements. Then you go back and analyze the possible upper environments for those areas. At some point an operational will start picking up on any one sig. At that range it is still a crapshoot, however. You're just looking for more potential area of interest and then analyze the pattern to keep looking for something to rear its ugly head in the ops.
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Speaking of ensembles... [emoji102]
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Then you would be failing to see or underselling the favorable atmospheric conditions that were developing over Hanna and over the western GOM. It just ran out of time to see that potential through.
