Windspeed
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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.
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That already occurred the last week of July and first week of August. We had a two week stretch that had two hurricane landfalls. Were conditions perfect for a major? No, but Hanna would have been a major given 6 to 12 more hours over the western GOM. It was a very well-developed hurricane intensifying right up to landfall with a symmetrical eyewall. Would that being a major hurricane at landfall really change the conversation about this quieter stretch? Not really in my opinion. We'd still have some struggling systems until conditions flip to more favorable in the coming weeks. Again, it's August 13th.
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Are you seriously asking that question? Do you even read this thread? lol... Hell.... Kill me...
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TAFB/NHC has issued a code yellow for a weak disturbance near the North Carolina coastline that is forecast to move ENE in the coming days with 20/30 probs. It does have weak mid-level vorticity and could take on more tropical characteristics in the coming days as the system moves out into the open Atlantic. ZCZC MIATWOAT ALL TTAA00 KNHC DDHHMM Tropical Weather Outlook NWS National Hurricane Center Miami FL 200 PM EDT Thu Aug 13 2020 For the North Atlantic...Caribbean Sea and the Gulf of Mexico: The National Hurricane Center is issuing advisories on recently upgraded Tropical Storm Josephine, located over the tropical Atlantic Ocean several hundred miles east of the Lesser Antilles. 1. A low pressure area over eastern North Carolina is expected to move east-northeastward across the north Atlantic well to the south of New England and the Canadian Maritime provinces for the next several days. This system could acquire some subtropical or tropical characteristics during the next two to three days while it moves over warm sea surface temperatures. * Formation chance through 48 hours...low...20 percent. * Formation chance through 5 days...low...30 percent. Forecaster Beven
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Has anyone said it was? Seems like most, including myself in recent posts, have gone to great lengths to cite the differences. Yet, ACE is still more than double climatological average for this date. It's also just Aug. 12th and we've had two hurricane landfalls in 2020 in addition to an ongoing TCG during an unfavorable period. You keep harping a specific operational model, in this case the GFS in the long-range, over and over again. I am uncertain why you are trying to climb upon this hill which to die. It's premature to do so a month prior to climatological peak. Counter arguments already established in this thread that we are in a less active period. It is too early to be locking down on a 240+ long-range operational output to make heads or tales of what will or will not occur versus just utilizing climatological modeling tools that such scenarios are better intended and better suited, such as ensemble precipitation guidance, long-range pattern and oscillation modeling, which do suggest a ramp up of activity across the Atlantic Basin in a few weeks.
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Last night's ECMWF ensembles were picking up on a AEW in the 7-10 day range and developing it near the Northern Leeward Islands. To be honest, the operationals have not been the greatest this year on TCGs. The GFS op even ghosted a CA monsoonal gyre last week and went so far to produce a fantasy GOM hurricane over many consecutive runs. Odd fantasy TCGs aren't unusual, but entire monsoonal gyres are. They also have not handled positioning of upper 200 hPa vorticity well for convection. So the GFS may've just had that too far displaced east over the Caribbean. WPAC TCG has been off as well in the operationals. At any rate, complaining aside, I'm not sure if it's a lack of global flight data or just bad luck. We're still in the long range for improving pattern and environmental factors in the 10+ day range, however. You want to focus more on ensembles in the long-range and ops for short-term TCG. But even in the short-term, the ops haven't been great.
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Isaias was a fast mover and the depth of the 26° isotherm is very anomalous off the SE CONUS this year. It's been a very hot Summer with limited cloud cover and few stalled boundaries, especially over the past 30-40 days. Everything on the shelf is above 26°C now based on AOML; and since the shallow layer for SSTs is only 25-30 meters at depth, it essentially is anomalously warm right up to the shoreline. Though keep in mind, the isotherm map isn't on the same scale, as the shallow shelf is only 50 meters deep at interaction with the Gulf Stream, where, at that point, it drops well below 100 meters on a much higher gradient extending ESE. This may also be throwing off the TCHP map as depth of 26ºC isotherm is one of the data sets along with immediate surface layer temperature profiles. In past years, the shallow shelf was hardly represented by the 26º isotherm. Perhaps in recent years this was changed in the way data was displayed; however, if the entire shelf is above that isotherm, it should still be represented in the immediate surface layer at ~30 meter estimate. Though Isaias' low level circulation was amplified by a tropical low level southerly jet on its eastern semicircle due to trough interaction, it was really moving too fast and had too small an RMW to do anything but perhaps upwell and push ~28°C water from 50+ meters depth down the shelf near the Gulf Stream. The immediate landfall area did cool a few degrees, but that appears to be rebounding fast due to hot days + clear skies. Also recall that Isaias only managed to regain hurricane intensity very near the South Carolina shoreline. Additionally, it remained rather devoid of convection on its southern semicircle and struggled to mix down higher winds until interaction with the coast. Its windfield only expand near landfall with influence of the low level jet and baroclinic enhancement up the Mid-Atlantic coast. In comparison, Hanna was a slow mover with a much broader low level circulation as it traversed the Central GOM and had a large region of persistent intense multi-convective systems that did a number on the shallow layer heat content, not to mention some extended upwelling. But that's been several weeks ago and, unsurprisingly, the Central and WGOM immediate shallow layer is running ~29-31°C again.
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In a meteorological sense, it's called oceanic lag time. The ocean heat content always lags behind atmospheric mean temperature gain. It also takes time, even in the most favorable large scale patterns, for hurricane season to reach fruition.
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If I read you right, you're calling for 2 hurricanes and 1 major hurricane the remainder of the season? I mean that's fine but you realize it's August 12th? Climatological favorability across the basin doesn't normally kick in until around August 20th-26th even in active years. I think a lot of folks fail to realize how quickly an unfavorable synoptic and environmental pattern can transition to favorable. Shear issues appear to be short-term. The hostile westerly upper level flow across the Caribbean is due to the current convective outbreak in the Eastern Pacific. However, more favorable upper 200 hPa vorticity will shift to over the Atlantic Basin by August 20th. Westerly windshear will decrease as the EPAC swings into a more suppressed regime. Likewise the strong easterly 700 hPa windbursts that have driven SAL will back down as Azores SPHP shifts into a more SER/WAR extended pattern (as is typical does this time of year). As such, the MDR will moisten for the September run. Sub-800 hPa to sea level pressures have already been running lower than climatological mean. All these factors within consideration, I think some folks are going to be taken surprise during the peak regardless of the active to hyperactive forecasts.
