KoritheMan's WunderBlog

Tropical weather analysis - May 28, 2014

By: KoritheMan, 3:05 AM GMT on May 29, 2014


Amanda is on a continued weakening trend as of the 0300Z NHC advisory:

Wind: 45 mph, with higher gusts
Location: 16.3°N 111.3°W
Movement: NE at 6 mph
Pressure: 1004 mb

Amanda came in like a wrecking ball, and is now being wrecked by the wrecking ball*. While the 0z satellite estimates support a somewhat stronger storm -- closer to 45 kt -- the NHC has chosen, perhaps rightfully, to lower the intensity a bit below the Dvorak estimates, which do not fare as well with quickly decaying tropical cyclones. The cloud pattern is very disorganized, and I am having a lot of difficulty in following a coherent center. Based primarily on extrapolation and some recent microwave imagery, as far as I can tell the low-level center is well southwest of the vigorous mid-level center seen in satellite imagery within the convection. While recent UW-CIMSS shear analyses show the shear has decreased to 20 kt and is slowly decreasing to the north of Amanda, it is still currently fairly strong, and even if it does decrease it will be too little too late.

*Credit goes to wunderkidcayman for letting me use that analogy in his own words.

Figure 1. Latest infrared satellite image of Tropical Storm Amanda. Image credit: NOAA's Satellite Services Division (SSD).

Amanda is likely to continue weakening, and my forecast of dissipation as a tropical cyclone by 72 hours may be a generous one. Water vapor imagery and CIMSS TPW data show a substantial amount of dry air in the near-storm environment, with arc clouds continuing to expand outward away from the center in the southern and western semicircles. The dry air, shear, and inherently disorganized structure should lead to continued weakening, with Amanda dropping below tropical storm strength in about 36 hours, if not sooner. If current trends continue, Amanda could dissipate in as little as 24 to 36 hours. Even though the shear is forecast to decrease in about 36-48 hours as a large anticyclone develops aloft, dry air continues to channel down the Pacific off the coast of California along the backside of an upper-level trough. While this dry air is not yet at the longitude of the tropical storm, it will probably get there by the time Amanda weakens to a tropical depression, worsening the already meager thermodynamic conditions that prevail in the path of the cyclone. The GFS and ECMWF show a residual surface low persisting the low-level flow for several days subsequent to dissipation, but this could very well be a generous prognostication given the harsh environment. SSTs along the path of Amanda appear to have warmed some over the last couple of days, and should remain in the 27 to 27.5C range throughout the forecast period barring any significant track changes. Despite the adequate SSTs, dry air will continue to be a problem for Amanda even as the shear decreases; further, it is unlikely Amanda will be able to realign itself with the more favorable conditions given its currently disheveled state.

The cyclone appears to be moving a little bit to the left of what was expected in the 5 PM NHC advisory, but that is admittedly difficult to gauge given the disorganized and elongated nature of the vortex. Part of this seemingly more westward movement could be due to the lack of convection, with UW-CIMSS steering data indicating more ridging at 850-700 mb than at 700-500 mb. Water vapor imagery shows a broad downstream upper trough stretching from the northwestern United States southwestward to the eastern north Pacific. The southern portion of this trough is fracturing, while the northern portion moves eastward. As this trough flattens out over the next couple of days, Amanda is expected to have its poleward progress blocked, come to an abrupt halt, and then reverse its course to a west-southwesterly or southwesterly direction as a lower-tropospheric ridge rebuilds to the north of the tropical storm. The guidance is in good agreement on the turn, with the large differences over the past few days in regards to the magnitude and timing of no longer evident. My forecast follows closely the GFS and ECMWF, which are currently not too dissimilar. It is possible that Amanda could move more slowly than forecast once the trough lifts out, particularly if it continues its abrupt decaying trend.

Intensity forecast

Initial 05/29 0300Z 40 kt 16.3°N 111.3°W 45 mph
12 hour 05/29 1200Z 35 kt 16.4°N 110.9°W 40 mph
24 hour 05/30 0000Z 35 kt 16.9°N 110.1°W 40 mph
36 hour 05/30 1200Z 30 kt 17.6°N 109.5°W 35 mph
48 hour 05/31 0000Z 30 kt 18.2°N 108.8°W 35 mph
72 hour 06/01 0000Z 25 kt 17.7°N 109.8°W 30 mph...post-tropical/remnant low
96 hour 06/02 0000Z 25 kt 17.0°N 111.0°W 30 mph...post-tropical/remnant low
120 hour 06/03 0000Z 20 kt 16.3°N 112.6°W 25 mph...post-tropical/remnant low

Track forecast

Figure 2. My forecast track for Amanda. My track was made using the initial position from the 5 PM NHC advisory. Since then, a new advisory has been released, so the initial position is off a little, but the overall track forecast philosophy remains the same.

Western Caribbean tropical trouble

There hasn't been much change to the model guidance in regards to the possibility of tropical mischief originating in the western Caribbean next week. The operational GFS and the ensembles continue to insist on the coalescing of a broad area of low pressure in the western Caribbean Sea moving northward into the Gulf of Mexico next week, at times as a tropical cyclone. The GFS shows a relaxation of upper-tropospheric winds beginning in the northwestern Caribbean east of the Nicaragua/Honduras border in about 6 - 7 days in response to a broad upper ridge, likely attributable at least in part to the release of latent heat from the increased thunderstorms in the western Caribbean/eastern Pacific region associated with two westward-moving tropical waves enhancing large-scale cyclonicity. This is a classic development pattern for early June, and this is also a climatologically-favored location for homegrown early-season development. The first tropical wave is moving across the Panama/Costa Rica region into the southwestern Caribbean Sea, while the other is moving through Venezuela and the eastern Caribbean waters. Global model guidance shows that the majority of energy associated with the first wave will likely affect the eastern Pacific waters, but enough energy could be left behind to leave a trail of preexisting cyclonicity pending the arrival of the second wave, which is forecast to head northwestward and affect primarily the western Caribbean. The result could be the formation of a broad area of low pressure. Right now it still more likely than not that no tropical development occurs, and instead we get stuck with a period of multi-day heavy rainfall for the western Caribbean, with the possibility of an embedded surface low somewhere within the gyre; based on the GFS shear forecast, climatology, and the location of the tropical waves, I feel that any surface low that may develop would likely do so east of the Nicaragua/Honduras line.

While tropical development still appears pretty unlikely given the modeled timeframe of Arthur forming is still about a week out, residents of the western Caribbean can certainly anticipate a multi-day heavy rainfall event, an event that may cause flooding in some of the mountainous regions of the affected countries, particularly Honduras and Nicaragua. If any tropical cyclone does develop, it will likely move north into the Gulf of Mexico, where upper-level winds will likely keep it a lopsided cyclone with the heavy rain and gusty winds to the east of the center.

2014 Pacific hurricane season Tropical Storm Amanda 2014 Atlantic hurricane season

Updated: 3:20 AM GMT on May 29, 2014


Tropical weather analysis - May 27, 2014

By: KoritheMan, 2:28 AM GMT on May 28, 2014


Hurricane Amanda remains a Category 2 hurricane according to the 5 PM NHC advisory:

Wind: 105 mph, with higher gusts
Location: 15.0°N 112.6°W
Movement: NNW at 5 mph
Pressure: 970 mb
Category: 2 (Saffir-Simpson Hurricane Wind Scale)

The overall convective canopy has shrunk compared to 24 hours ago, but Amanda is still producing some cold-topped thunderstorms near the center; additionally, evening microwave data does not show too large a vertical displacement, heralding a possible small decrease in southerly shear. The shear is still strong, however, as storm-relative water vapor imagery doesn't show much evidence of upper-tropospheric outflow in that direction. UW-CIMSS ADT estimates still support an intensity close to 90 kt, but recent SAB numbers have been dropping. Regardless, Amanda is probably not a Category 2 anymore, with recent microwave data no longer showing evidence of an eye, even aloft.

Figure 1. Latest infrared satellite image of Hurricane Amanda. Image credit: NOAA's Satellite Services Division (SSD).

The future intensity of Amanda is uncertain. On one hand, the displaced but not too heavily of the low- and mid-level centers suggests that Amanda may be warding off the shear, at least for now. On the other hand, water vapor and satellite data show arc clouds over the southern portion of the circulation, coincident with a moisture minimum on CIMSS Total Precipitable Water (TPW) images. Since there is still some decent shear in the near-storm environment, the current possible decrease notwithstanding, the hurricane could very easily ingest this dry air and hasten the weakening process. In addition, Amanda is headed for a region of progressively cooler sea surface temperatures, and as mentioned by the National Hurricane Center earlier, an objective glance at the regional SSTs suggests that the SST input into the SHIPS model could be about 1C too high, giving the statistical models a high bias during this decaying portion of the storm. My forecast is weighted more heavily toward the global models, which are probably handling this particular situation with more accuracy. I still expect Amanda to dissipate as a tropical cyclone by day five, although I have been gradually pushing this back day by day. It should be noted that the GFS/SHIPS suggests that the shear has already plateaued, and should be steadily decreasing from this point out as a small upper low seen in water vapor imagery to the northwest of the hurricane continues to pull away to the north. Indeed, the GFS averaged 850-200 mb vertical shear algorithms show a substantial decrease in shear as Amanda moves northward, but the marginal thermodynamic environment characterized by cool SSTs and associated stable air should preclude any restrengthening during the next few days. If Amanda resists the unfavorable environment during the next few days, it could begin to restrengthen during the long-term, but this is not shown in any of the guidance at this time.

Synoptic data suggest that Amanda is well-embedded in southerly cyclonic flow on the east of a retrograding mid- to upper-level low, the same one responsible for the shear. As another trough amplifies over the northwestern United States and moves eastward, the global model 500 mb geopotential height fields show the subtropical ridge remaining open; probably not enough to induce full on recurvature, which indeed none of the guidance shows, but certainly enough to prevent an immediate westward motion before the trough lifts out in about 48 hours. Beyond that time, the guidance unanimously turns Amanda westward and southwestward under a building lower-tropospheric ridge, with the only differences being on the sharpness of the turn, as well as the location and timing of it. The GFS shows Amanda turning around 17N, while the CMC shows the cyclone getting near Baja and not turning until 22N. The latter model appears to be falsely inflated with an overly enthusiastic strengthening episode that does not appear warranted, so my forecast is weighed more heavily toward the weaker GFS/ECMWF solution, but I am farther south of even those models as I simply do not foresee Amanda persisting with much convection in the harsh thermodynamic environment that awaits. If Amanda proves to be her typical tenacious self, the cyclone would likely track to the right of my current forecast, possibly even delaying the onset of the southwestward turn by a bit.

Residents of Baja may feel some increased surf and high clouds by late week, but Amanda is not likely to make landfall there, or even come close to the peninsula proper.

Intensity forecast

Initial 05/28 0000Z 15.0°N 112.6°W 90 kt 105 mph
12 hour 05/28 1200Z 15.7°N 112.5°W 75 kt 85 mph
24 hour 05/29 0000Z 16.4°N 112.4°W 65 kt 75 mph
36 hour 05/29 1200Z 17.3°N 111.9°W 55 kt 65 mph
48 hour 05/30 0000Z 18.1°N 111.6°W 45 kt 50 mph
72 hour 05/31 0000Z 17.8°N 112.2°W 35 kt 40 mph
96 hour 06/01 0000Z 17.4°N 112.7°W 30 kt 35 mph
120 hour 06/02 0000Z 16.7°N 113.6°W 25 kt 30 mph...post-tropical/remnant low

Track forecast

Figure 2. My forecast track for Amanda.

Western Caribbean to be monitored next week

For the last week or so, the operational GFS, along with some of its ensemble members, have been indicating anything from an increase in tropical moisture in the western Caribbean waters to a full-fledged tropical cyclone moving northward out of the Caribbean. The catalysts intended to trigger this complex pattern may be related to two tropical waves currently moving across the Atlantic Ocean as denoted on the 18z NHC surface map (shown below).

Figure 3. 18z surface analysis map from the National Hurricane Center (NHC). These graphics are intended to compliment and supply additional information to the text-based Tropical Weather Discussion (TWD), which thoroughly discusses large-scale meteorological features over the Atlantic, Caribbean, and Gulf of Mexico waters.

As you can see, there are currently three distinct tropical waves moving across the Atlantic as per the graph. The one in the far east of the image is probably inconsequential in this particular case unless it accelerates, as it typically days 10 days for a tropical wave to reach the western Caribbean from the coast of Africa and sometimes longer. The ones I think will go on to instigate the area of disturbed weather shown by the GFS and its ensembles are the two tropical waves farther to the west. The first is currently moving across the southern Caribbean across South America, and is progged by the models to eventually enter the eastern Pacific in about a day or two, likely enhancing convection behind the wave axis. While the majority of the energy associated with this wave will probably more strongly influence the eastern north Pacific, at least some residual lower- to mid-tropospheric cyclonicity appears likely to affect the western Caribbean waters. Although upper-level winds are not currently favorable, another tropical wave closely trailing the aforementioned one is about to enter pass through the Windward Islands during the next 12-24 hours, and it appears this wave may be the one that could trigger the formation of a broad surface low pressure area, as has been hinted at by the GFS and its ensembles for quite awhile.

While we by no means have run-to-run consistency on a tropical cyclone, the general modeled expectation has been for a large area of increased moisture/possible broad surface low to develop in the western Caribbean during the first few days of June as high pressure builds over the Great Lakes/Ohio Valley region. This is a classical pattern that tends to focus low-level convergence in the waters of the western Caribbean, a climatologically-favored breeding ground for early-season tropical cyclone development. It is too early to speculate on where this potential area of disturbed weather might eventually go, but everyone in the western Caribbean and along the Gulf Coast should start watching this area more closely next week.

Chances are still better than not that a tropical cyclone does not form from this area, but coincident with the upward MJO sending at least a weakly positive signal, it's not something that can be ignored. Regardless of whatever development may occur, residents in Cuba, the Yucatan Peninsula, the Cayman Islands, Jamaica, and even portions of Central America can anticipate a multi-day period of heavy rainfall beginning late this week extending into next week.

2014 Pacific hurricane season Hurricane Amanda 2014 Atlantic hurricane season

Updated: 2:40 AM GMT on May 28, 2014


Tropical weather analysis - May 26, 2014

By: KoritheMan, 2:27 AM GMT on May 27, 2014


Amanda is on a weakening trend. As of the 5 PM NHC advisory from the National Hurricane Center, the following information was posted on the hurricane:

Wind: 120 mph, with higher gusts
Location: 13.4°N 111.8°W
Movement: NNW at 5 mph
Pressure: 957 mb
Category: 3 (Saffir-Simpson Hurricane Wind Scale)

Since the advisory, the hurricane has degraded a bit in appearance, but in general, Amanda is tenaciously holding its own. A cloud-filled and ragged eye has been periodically visible beneath the convective canopy in infrared satellite images, but it disappeared from the visible around 0000 UTC culminating with a convective burst. Recent UW-CIMSS Total Precipitable Water (TPW) observations show an abundance of dry air/subsident flow to the west, but this appears to be largely unaffecting the core at this time. Upper-tropospheric outflow remains well-established in all quadrants but the south, where it continues to be restricted by 25 kt of southerly vertical wind shear as denoted by UW-CIMSS wind shear analyses. This shear has caused some semblance of vertical tilting to the low- and mid-level centers as denoted in recent SSMIS microwave data.

Figure 1. Latest infrared satellite image of Hurricane Amanda. Image credit: NOAA's Satellite Services Division (SSD).

The shear is being caused by a combination of a downstream amplifying upper-level trough and the strong subtropical ridge to the east of Amanda. There are some indication in the model fields that the 850-200 mb averaged vertical shear over the hurricane could decrease a little with time, particularly between the 48 and 72-hour mark and continuing thereafter as a diffluent and possibly weakly anticyclonic environment becomes more attuned and involved with the cyclone vortex, but the timing and magnitude of this decrease is uncertain. Even if it did materialize, Amanda will be traversing increasingly marginal water temperatures during that time, and the exposed and decaying state of the circulation that is likely during that time would allow for a good chunk of dry air to become entrained into the circulation from the stable Pacific marine layer to the west. I'm continuing to announce dissipation as a tropical cyclone by day five, but the global models suggest the residual surface low could persist for several more days in the low-level flow. Continued weakening is expected in the interim, but it could be slow given that Amanda is still over 28-29C SSTs and dry air does not appear to be afflicting the inner core convection at this time.

Amanda continues moving steadily to the north-northwest, squeezed between a persistent subtropical ridge to the east and a developing upper-level trough to the west. Excluding the GFS which appears to not be handling the initial motion particularly well, my forecast is weighted heavily toward a consensus of the models, with particular weight on the ECMWF except near the end of the forecast period when I anticipate a slow westward turn beginning as a decadent Amanda feels the influence of the lower-level trades. Very slow and erratic motion is possible as early as day four, particularly if Amanda weakens quicker than predicted. The models show the system meandering in the vicinity of Socorro Island for several days as a dissipating remnant low.

Intensity forecast

Initial 05/27 0000Z 13,4°N 111.8°W 105 kt 120 mph
12 hour 05/27 1200Z 14.1°N 112.1°W 90 kt 105 mph
24 hour 05/28 0000Z 14,8°N 112.4°W 80 kt 90 mph
36 hour 05/28 1200Z 15.7°N 112.3°W 60 kt 70 mph
48 hour 05/29 0000Z 16.5°N 112.2°W 45 kt 50 mph
72 hour 05/30 0000Z 17.2°N 112.1°W 30 kt 35 mph
96 hour 05/31 0000Z 17.9°N 111.9°W 30 kt 35 mph
120 hour 06/01 0000Z 17.9°N 112.0°W 25 kt 30 mph...post-tropical/remnant low

Track forecast

Figure 2. My forecast track for Amanda.

Hurricane Amanda 2014 Pacific hurricane season

Updated: 2:29 AM GMT on May 27, 2014


Tropical weather analysis - May 26, 2014

By: KoritheMan, 7:01 AM GMT on May 26, 2014


Hurricane Amanda continues to spin harmlessly out to sea as a formidable major hurricane. As of the latest NHC advisory, the following information was posted on the hurricane:

Wind: 145 mph, with higher gusts
Location: 12.6°N 111.4°W
Movement: NNW at 3 mph
Pressure: 941 mb
Category: 4 (Saffir-Simpson Hurricane Wind Scale)

The satellite appearance of Amanda has deteriorated this morning. The central convection has become a bit more spread out and a little elongated, particularly over the southern quadrant due to the onset of southerly shear; in addition, satellite and microwave data throughout the evening suggests that the eye has shrunk compared to 12 hours ago, and there have been signals that the outer wind maxima may be stronger than the inner core convection. Indeed, latest satellite data suggest that the eye may be reappearing again concurrent with an increase in convection in the southwestern eyewall, but the location of the convection relative to the eye suggests that the radius of maximum winds may be increasing. The eye remains small and distorted, and could quickly collapse. It should be noted that the 6z satellite estimate from SAB has increased a bit to 6.5, which would support a continued intensity of 125 kt. On the other hand, adjusted T numbers using the CIMSS Advanced Dvorak technique yields a current estimate of around 115 kt. I'm not impressed with the SAB estimate, and the CIMSS ADT estimate seems more reasonable.

Figure 1. Latest infrared satellite image of Hurricane Amanda. Image credit: NOAA's Satellite Services Division (SSD).

Although Amanda is still moving over very warm waters, the latest Reynolds sea surface temperature analyses indicate that waters have cooled a bit under the hurricane, suggesting the possibility of cold water upwelling; this is especially possible since Amanda is actually moving even slower than it was 24 hours ago. Additionally, the latest UW-CIMSS shear analyses shows me there is 25 kt of southerly shear over Amanda, and indeed the outflow has become squashed in that direction. However, Amanda is moving somewhat parallel with the shear vector, and this could mitigate as much weakening as would normally occur under such a pattern. The GFS shows shear remaining in the 25 to 30 kt range over the next 72 hours or so, but I am not too eager to announce too abrupt of a demise until the onset of recurvature, when Amanda is likely to move over increasingly marginal waters and entrain the stable marine layer intrinsic to this portion of the Pacific. Interestingly, the GFS shows an upper ridge building over Amanda after 72 hours, culminating in the onset of much lower wind shear, but it will simply be too little too late. The global models now show the cyclone dissipating as a tropical cyclone by day five, and this is reflected in my own forecast as well. It is possible that Amanda could weaken faster than I am expressing, especially at 72 hours and beyond as it comes under the influence of the aforementioned negative thermodynamics.

After wobbling a bit to the north a few hours ago, Amanda appears to have resumed a slow north-northwest motion. The global and dynamical guidance presume that a general northwest to north-northwest motion will continue through a general weakness in the subtropical ridge caused by a slow-moving shortwave trough over the southern Rockies/west Texas area. This synoptic feature is progged by the models to gradually swing eastward, but should stick around long enough to, in tandem with a second, more distant upper trough off the northwestern United States, influence the ridge enough to keep a persistent weakness in it, while also strengthening the subtropical ridge to the east of Amanda. Later in the period, the Pacific trough is forecast to dive southeastward closer to a rapidly weakening Amanda and induce full recurvature. The ECMWF continues to be slower than the GFS and farther to the east, with the latter model continuing to take a decaying Amanda near southern Baja, but the overall model consensus hasn't budged. It is possible that the cyclone could move even slower near the end of the forecast period, especially if it weakens quicker than I am predicting.

As a bit of trivia, Amanda is the strongest eastern north Pacific hurricane on record for the month of May, surpassing the previous record of 125 kt/145 mph set by Hurricane Adolph in 2001. Also, if the National Hurricane Center analyzes Amanda as a 140 kt/160 mph storm during post-season analysis, it would be the first instance of a Category 5 occurring in the eastern north Pacific during the month of May. The current earliest Category 5 holder remains Hurricane Ava of 1973, which became a Category 5 on June 6.

Intensity forecast

Initial 05/26 0600Z 12.8°N 111.5°W 125 kt 145 mph
12 hour 05/26 1800Z 13.3°N 111.7°W 110 kt 125 mph
24 hour 05/27 0600Z 13.9°N 112.0°W 90 kt 105 mph
36 hour 05/27 1800Z 14.8°N 112.4°W 75 kt 85 mph
48 hour 05/28 0600Z 16.0°N 112.6°W 65 kt 75 mph
72 hour 05/29 0600Z 17.2°N 112.3°W 45 kt 50 mph
96 hour 05/30 0600Z 17.9°N 111.7°W 35 kt 40 mph
120 hour 05/31 0600Z 18.5°N 111.2°W 30 kt 35 mph: post-tropical/remnant low

Track forecast

Figure 2. My forecast track for Amanda.

Hurricane Amanda 2014 Pacific hurricane season

Updated: 8:17 AM GMT on May 26, 2014


Tropical weather analysis - May 25, 2014

By: KoritheMan, 6:04 AM GMT on May 25, 2014


Amanda has quickly become a major hurricane. As of the latest NHC advisory, the following information was posted on the storm:

Wind: 115 mph, with higher gusts
Location: 11.6°N 110.7°W
Movement: WNW at 5 mph
Pressure: 966 mb
Category: 3 (Saffir-Simpson Hurricane Wind Scale)

As was been noted -- both by myself and the National Hurricane Center -- there was always an extant possibility of Amanda rapidly intensifying. Although it has its moments in terms of measurable error and false alarms, I simply have to give credit to the SHIPS for correctly anticipating the very favorable atmospheric and oceanic conditions that led to this abrupt burst of strengthening. The satellite signature is remarkable, with a well-defined 10 to 15 mile-wide eye enveloped by a closed circle of cold convection demarcating the boundaries of the hurricane's central dense overcast (CDO). The most recent raw t number from the UW-CIMSS ADT algorithm is at 7.0, or 140 kt; Category 5. However, the raw t number isn't a reflector of the actual intensity, and is entirely based on current cloud structure yielding a satellite classification that is unadjusted for bias and error. Recent adjusted t numbers using the CIMSS satellite technique is about 5.7, closer to 105 kt, suggesting that Amanda could be a little stronger than the current 0300Z NHC intensity estimate.

Figure 1. Latest infrared satellite image of Hurricane Amanda. Image credit: NOAA's Satellite Services Division (SSD).

Amanda is still over 29°C sea surface temperatures and within a moist environment characterized by light vertical shear. These synoptics should prevail for at least the next 24 hours, and possibly up to 36 hours since the SHIPS only shows underlying water temperatures decreasing by .3°C from their current value of 29.3°C as per the 0z diagnostic file attendant to that model. In addition to the aforementioned, water vapor imagery suggests a near-equatorial ridge in the central Pacific that appears to be enhancing the equatorial outflow, along with an accompanying jet streak associated with a distant upper trough to the north amplifying the poleward outflow. This favorable upper flow pattern should enable additional intensification before southwesterly shear increases sharply and SSTs cool gradually in about 36-48 hours. My forecast is higher than virtually all of the available intensity guidance as of 0z, and shows Amanda peaking as a low-end Category 4. I left the intensity steady from the 24 to 36 hour mark due to a continued strongly divergent upper tropospheric flow, and also because I still don't think the entirety of the shear during this period will be completely disconnected from Amanda's own outflow. A very quick and cruel demise is anticipated by the end of the forecast period as the shear increases to over 30 kt, water temperatures cool to 26-27°C, and subsident flow aloft associated with the eastern Pacific marine layer becomes entrained into the cyclone circulation.

Satellite data suggests that Amanda remains essentially on track with the current NHC track prediction, continuing a slow and general west-northwest motion. Water vapor imagery shows the shortwave trough over the southwestern United States is moving eastward away from the longitude of the hurricane. However, the trough is moving extremely slowly, and the global model guidance suggests it will still be in the Louisiana region in 3-4 days. This evolution should keep enough of a weakness in the subtropical ridge to the east of Amanda to continue a uniform poleward motion. A turn toward the north is anticipated beyond 24 hours as the hurricane comes under increasing southerly flow. The GFS is faster than the ECMWF today, which is a reversal of their respective inclinations yesterday. The ECMWF solution is likely based on a shear-apart-and-stall scenario off Baja California, a situation that does not look especially unlikely. My forecast will not fully commit to a sharp eastward turn at the end of the forecast period, comprising instead between the two aforementioned possibilities. The global models show Amanda's low-level center disintegrating off the coast while the mid and upper-level centers race northeastward toward the trough. This should protect Mexico from any potential long-range threats.

Amanda is the second earliest-forming major hurricane in the eastern Pacific basin, behind Hurricane Bud in 2012.

Intensity forecast

Initial 05/25 0300Z 11.6°N 110.7°W 100 kt 115 mph
12 hour 05/25 1200Z 11.8°N 111.2°W 110 kt 125 mph
24 hour 05/26 0000Z 12.5°N 112.6°W 115 kt 135 mph
36 hour 05/26 1200Z 13.3°N 111.9°W 115 kt 135 mph
48 hour 05/27 0000Z 14.4°N 112.4°W 105 kt 120 mph
72 hour 05/28 0000Z 15.3°N 112.6°W 75 kt 85 mph
96 hour 05/29 0000Z 16.6°N 112.4°W 45 kt 50 mph
120 hour 05/30 0000Z 18.1°N 112.2°W 25 kt 30 mph

Track forecast

Figure 2. My forecast track for Amanda.

Hurricane Amanda

Updated: 6:10 AM GMT on May 25, 2014


Tropical weather analysis - May 24, 2014

By: KoritheMan, 6:27 AM GMT on May 24, 2014


Tropical Storm Amanda continues to intensify as of the latest NHC advisory:

Wind: 60 mph, with higher gusts
Location: 11.2°N 109.1°W
Movement: WNW at 5 mph
Pressure: 1000 mb

Satellite and microwave data suggest that Amanda is forming an inner core, with a mid-level eye featured observed on the most recent SSMIS microwave pass (0233Z). The lower- and mid-tropospheric circulations also appear to be better collocated than they were 24 hours ago, suggesting a decrease in southerly shear. There is a prominent rainband to the north of the system.

Figure 1. Latest infrared satellite image of Tropical Storm Amanda. Image credit: NOAA's Satellite Services Division (SSD).

With a formative inner core, Amanda should have no trouble intensifying, with the SHIPS rapid intensification parameter intrinsic to that model postulating a 66% chance of a 25-kt increase in wind speed during the next 24 hours, and even a 47% chance of a 40-kt increase during the same period. While Amanda isn't in a hurry to go anywhere, the underlying waters are around 29°C and extend to great depth; this is common of the eastern north Pacific basin even as early as the month of May, and I do not anticipate cold water upwelling to be a significant factor for Amanda's future intensity. The only potential negative to continued intensification -- quite possibly rapid -- is a small area of dry air noted to the west of the center on CIMSS Total Precipitable Water (TPW) imagery (shown below). If this subsident flow were to work its way into the cyclone center, it would likely significantly offset future intensification potential and the possible rapid intensification that could be starting. However, there is not much evidence of dry air entrainment on satellite images at this time, and I am assuming this will continue to be the case.

Figure 2. 0100Z Total Precipitable Water (TPW) image of the eastern Pacific. I took the liberty of delineating arrows pointing to both the approximate center location of Amanda, as well as the nearby subsident flow aloft leading to dry/sinking area just to the west of the storm center. There is a small dry slot evident in the western periphery of the cyclone circulation as identified on the image. While there's no strong evidence of this occurring on current satellite imagery, entrainment of such an airmass would likely preclude the possibility of rapid intensification, and potentially have significant effects on long-term intensity change. Image credit: University of Wisconsin Cooperative Institute for Meteorological Satellite Studies (CIMSS).

If everything goes well, Amanda could approach the threshold of major hurricane (Category 3+) strength in about 48 hours. My forecast shows a peak of 90 kt during that time, and is higher than most of the guidance. The GFDL takes Amanda to 90 kt near that time period, following close behind the HWRF which brings the cyclone up to 94 kt in roughly 36 hours. Beyond the 48 hour timeframe, the guidance shows an increase in southwesterly shear as an upper-level trough amplifies downstream from the tropical cyclone. While some of this shear -- at least initially -- could be related at least a little to the outflow from a then powerful hurricane, a good dose of it will come from the trough. The shear is forecast to increase farther near the end of the forecast period, which along with progressively cooler waters along the forecast track should begin to weaken Amanda. It is possible that Amanda could weaken more rapidly than shown here by days four and five, especially if any significant increase in vertical shear occurs and exposes the circulation enough to dry air connected with the eastern Pacific marine layer. It is equally possible Amanda could intensify more than forecast through 48 hours and become a major hurricane, but the best course of action is to remain conservative until a more definitive rapid intensification trend becomes actual.

Amanda appears to be on track with the NHC forecast track, and its motion is consistent with the large-scale pattern enveloping the cyclone. Amanda is situated between a mid-level ridge to the east and a mid- to upper-level trough to the north over the southwestern United States. Water vapor imagery already shows the trough moving eastward, with the northerly flow slowing and trailing behind it indicating it may not make much farther southward progress. This is consistent with the global model guidance which shows the subtropical ridge gradually rebuilding to the north of Amanda and maintaining the generally west-northwestward track. In about 72 hours or so, Amanda is forecast to turn northward ahead of an approaching upper-level trough. The GFS and ECMWF have come northward relative to my previous forecast, and tonight's forecast was adjusted significantly poleward.

It's interesting to note that the GFS and HWRF show a sort of shear apart and stall scenario occurring by the end of the forecast period, which could very easily happen if southwesterly shear gets the best of Amanda. I have to acknowledge this possibility given our admittedly limited skill in evaluating tropical cyclone intensity change. For now, however, my forecast is weighed more heavily toward the stronger and faster ECMWF. Interests in southern Baja California and southwestern Mexico should monitor the long-range progress of Amanda, although I would be surprised if Amanda made landfall there as a viable tropical cyclone given the apparent environmental hostilities.

Intensity forecast

Initial 0600Z 05/24 11.2°N 109.1°W 50 kt 60 mph
12h 1800Z 05/24 11.5°N 109.7°W 60 kt 70 mph
24h 0600Z 05/25 11.8°N 110.5°W 70 kt 80 mph
36h 1800Z 05/26 12.1°N 111.0°W 80 kt 90 mph
48h 0600Z 05/26 12.4°N 111.6W 90 kt 105 mph
72h 0600Z 05/27 13.0°N 111.8°W 85 kt 100 mph
96h 0600Z 05/28 15.0°N 112.0°W 75 kt 85 mph
120h 0600Z 05/29 18.0°N 112.0°W 55 kt 65 mph

Track forecast

Figure 3. My forecast track for Amanda.

2014 Pacific hurricane season Tropical Storm Amanda

Updated: 6:36 AM GMT on May 24, 2014


Tropical weather analysis - May 23, 2014

By: KoritheMan, 5:48 AM GMT on May 23, 2014

Tropical Depression One-E

The persistent area of disturbed weather that everyone has been monitoring over the last several days has finally developed into a tropical depression. As of the second NHC advisory, the following information was delineated for this newly-developed system:

Wind: 30 mph, with higher gusts
Location: 10.6°N 107.8°W
Movement: WNW at 5 mph
Pressure: 1007 mb

Evening satellite analyses showing that the central convection connected with the tropical cyclone is currently a little thin, but this is probably a diurnal fluctation, as both water vapor imagery and UW-CIMSS Total Precipitable Water (TPW) do not show a substantial amount of dry air in the region of the depression. There is a broken band to the east which will probably wrap cyclonically into the center during the overnight hours and with any luck for the depression, lead to intensification.

Figure 1. Latest infrared satellite image of Tropical Depression One-E. Image credit: NOAA's Satellite Services Division (SSD).

The last ASCAT pass to catch the system showed winds of no more than 20 to 25 kt; this was around 1630Z. On the positive side, the depression has a fairly well-organized low-level circulation, and the environmental shear appears to be reasonably low. The SHIPS/GFS suggest the shear will meander in the 10 to 15 kt range for the next day or so before lowering below 10 knots thereafter. In addition, objective sea surface temperature analyses indicate that the cyclone will have plenty of time over water temperatures of 28 to 29°C, with ample underlying heat content to support convective growth. The SHIPS forecasts the depression to become a hurricane in about 72 hours amidst a favorable environment, with the 12z ECMWF actually suggesting a central pressure below 975 mb beyond day five, which is a pretty impressive barometric representation on a global model. The rest of the guidance is less bullish, but the general consensus is for the cyclone to approach the threshold of Category 1 intensity in the 3/4 day timeframe. How much intensification depends on several factors, but the most important of them is how warm the underlying sea surface temperatures remain; the 0z guidance suite shifted northward from the 18z guidance suite, and if those trends persist, the depression will spend less time over warm water, particularly if it accelerates more than forecast. Also, the GFS forecast fields show 850-200 mb averaged vertical shear increasing from the southwest near the end of the 120 hour forecast period, which could be a mitigating factor; in deference to that and the possibility of cooler waters, I have opted to weaken the cyclone a bit by day five.

The depression is moving slowly toward the west-northwest, more or less on track with the official NHC prediction. Water vapor images show a downstream upper-level trough over the western United States/Baja California region digging southeastward toward the longitude of the depression. The global models forecast this trough to continue digging until around the 36-48 hour mark, at which point the subtropical ridge should gradually rebuild, resulting in a faster motion toward the west and then west-northwest. Both the GFS and ECMWF show a northward turn near the end of the period continuing beyond the 120 hour mark, but the GFS is by far the more northern of the two, taking a weakening cyclone toward southern Baja. While this is not impossible, it appears that the primary reason for the northward jog is connected more strongly to a strong subtropical ridge forecast to strengthen to the east of the depression as the aforementioned trough pulls out with time. I am having a hard time biting on this specific solution given such an unusually poleward track for this time of year. It'll be interesting to peruse the 0z ECMWF run.

My forecast track is fairly similar to the National Hurricane Center one.

Intensity forecast

Init 0300Z 05/23 10.6°N 107.8°W 25 kt 30 mph
12 hours 1200Z 05/23 10.8°N 108.3°W 30 kt 35 mph
24 hours 0000Z 05/24 11.4°N 109.1°W 40 kt 45 mph
36 hours 1200Z 05/24 11.9°N 109.7°W 45 kt 50 mph
48 hours 0000Z 05/25 12.2°N 110.2°W 55 kt 65 mph
72 hours 0000Z 05/26 12.3°N 111.1°W 65 kt 75 mph
96 hours 0000Z 05/27 12.5°N 112.2°W 65 kt 75 mph
120hours 0000Z 05/28 13.3°N 113.6°W 55 kt 65 mph

Track forecast

Figure 2. My forecast track for Tropical Depression One-E.

Tropical Depression One-E

Updated: 5:49 AM GMT on May 23, 2014


I can't get around the idea of sneaking things into conversation casually.

By: KoritheMan, 6:28 AM GMT on May 20, 2014

A little excerpt from a conversation me and my friend were having on Facebook:


My biggest thing is I don't know how to do it in a way that's not my own direct way. Like I told you on the phone, it makes asking important questions WAY difficult. Like the most recent example being my zone manager. I thought he was gay, and my friends thought so too. So I asked him. Privately, but I still asked him. I can't think of a good way to sneak that into conversation casually.


you don't
some things you have to wait for

Maybe it's just my background, but I just don't see the flaws in my particular methodology. Thoughts?


Do I show signs of Aspergers?

By: KoritheMan, 3:55 AM GMT on May 09, 2014

This has nothing to do with weather, but I don't care.

So, yeah. Topic/blog title. Opine me. I'm strongly leaning toward yes, and for what it's worth, two of my friends both say I exhibit all the classical symptoms of Asperger's, but at the lower end of the spectrum. The guy friend is engaged to someone who has Asperger's, so they're not talking out of their ass.

Anyone have any thoughts on this? Particularly those that know me well... based on what you've seen of me on the blogs (bearing in mind my internet persona is literally no different than it is real life... that's a farce I have no intention of erecting)... do I show these symptoms to you guys as well?


Tropical weather analysis - May 7, 2014

By: KoritheMan, 2:44 AM GMT on May 08, 2014

Invest 90E

A broad area of low pressure accompanied by widespread cloudiness and thunderstorms continues moving toward the coast of southern Mexico. In yesterday's forecast, I was pretty solidified that we would see Tropical Storm Amanda heading toward the coast, but instead the circulation was not as well-defined as I was led to believe, as evident by a 1623Z ASCAT pass, which I will happily display below.

Figure 1. A 1623Z ASCAT pass captured the disturbance. Notice the two competing areas of vorticity (the actual mean center is the swirl farther to the south), and the lack of a well-defined center within the disturbance.

Satellite images show an extensive area of convection, some of it fairly deep, but recent microwave data and last-light visible imagery suggest that the low-level center remains hoisted to the south of the most intense shower activity.

Figure 2. Latest infrared satellite image of Invest 90E. Image credit: NOAA's Satellite Services Division (SSD).

Upper-level outflow is becoming restricted to the south, signifying an abrupt but well-forecast increase in southerly shear; this is due an amplifying downstream upper-level trough. This upper-level trough is also forcing a severe weather episode across portions of the Rockies/central plains region, with a myriad of large hail reports. Anyway, the increase in shear is further evident with a homogeneous comparison of microwave data (shown below), with the most recent microwave data showing the mid- and upper-level circulations displaced quite a bit.

Figure 3. Homogeneous comparison of the 37 GHz and 91 GHz channels on the latest SSMIS microwave pass, taken at 0022Z (current time rounded is roughly 0130Z as of this writing). The 37 GHz channel is more sensitive to the lower levels, while the 91 GHz channel is more sensitive to the mid- and upper troposphere. The low-level center can be fairly easily identified in the first image roughly around 15.6N 106.1W. In the second image, the circulation is located closer to 16N 104.8W.

While the recent acceleration of the system theoretically leaves open the possibility of the lower- and mid-level centers becoming somewhat better aligned vertically again, shear over the system is already about 20 kt over the system, and the GFS/SHIPS assume it will increase to over 30 kt in the next 24 hours. There is no physical way the low-level center will bolster the accelerator to 30 kt during this period, so the end result is that we're left with the mid-level center rapidly racing northeastward across southern Mexico, enhancing precipitation and flooding in that area while the low-level center gets strung out, left behind, and gradually weakens at or near the coast tomorrow. Indeed, the global models have unanimously become less aggressive in terms of tropical cyclone development from this area, and it looks like 1990's Hurricane Alma will maintain the status quo of the recordholder for earliest formation of the first eastern Pacific named storm (May 14, tied with Tropical Storm Aletta's record set in 2012).

To add insult to injury, satellite data show arc clouds emanating westward away from the system, which is a classical sign of dry air entrainment, likely from the subsident portion of the upper-level trough, and probably exacerbated by the local marine layer.

Even if this system does somehow consolidate into a short-fuse tropical storm, environmental conditions are quickly becoming unfavorable for development as the system approaches the coast. Regardless of development, heavy rainfall and flooding remain a threat across southern Mexico, particularly over areas of enhanced terrain. Any threat of locally gusty winds will be extremely short-lived and diminishing at the time of arrival as the overall circulation decays under the increasing shear and land interaction.

Moisture from this system may interact with the approaching frontal boundary and enhance heavy rainfall over portions of the southern plains and possibly the upper midwest/Great Lakes region through the weekend.

Probability of development in 48 hours: 40%

Probability of development in 120 hours: 40%

2014 Pacific hurricane season Invest 90E

Updated: 2:50 AM GMT on May 08, 2014


Tropical weather analysis - May 6, 2014

By: KoritheMan, 2:28 AM GMT on May 07, 2014

Invest 90E

A broad area of low pressure is centered several hundred miles south of Manzanillo, Mexico. This disturbance garnered the attention of the National Hurricane Center today, in the form of an off-season Tropical Weather Outlook (TWO) issued at 1:20 PM PDT this afternoon. The actual discussion contained within said outlook I pasted below for reader convenience:

ABPZ20 KNHC 062017

120 PM PDT TUE MAY 6 2014





Following the low cloud lines via visible satellite imagery from 18z to 0z, I am convinced that the increasingly better-defined center is located more or less in the center of the convective mass, an assessment that merits additional weight coincident with extrapolation of a timely 2343Z SSMI microwave pass that was fortunate enough to just capture the center. While there are no signs of convective banding yet, there is some evidence that the outer convection of the circulation is attempting to cyclonically consolidate toward the center of the surface low. Upper-level outflow is radiating sprightly to the north and northwest of the system for several hundred miles.

Figure 1. Latest infrared satellite image of Invest 90E. Image credit: NOAA's Satellite Services Division (SSD).

There is some evidence that an upper-level anticyclone is beginning to become collocated atop the surface low, an environment conducive for additional organization. I've dropped an image below showing the difference in the upper wind pattern aloft comprising the period 1800Z to 0000Z. Both images are creations of the University of Wisconsin CIMSS group.

Figure 2. Homogeneous comparison of the upper-level wind flow around Invest 90E from 1800Z May 5 to 0000Z May 6. The outflow level is typically found around 200 mb, so the light blue barbs are the ones we care about the most. Notice the fanning out of those same wind barbs toward the north and northwest, indicating a lessening of the upper-level shear as the upper-level trough responsible for it over the last couple of days fills in advance of another trough approaching from California.

The SHIPS, which uses the GFS formula for its own forecasts, suggests an environment of warm sea surface temperatures and low vertical shear over the next day or two, with the possibility of shear increasing in about 24 hours. Looking at water vapor imagery, the shear downstream of the disturbance does not appear to be as inhibiting as it has been over the last couple of days, so it's possible that the shear could hold off a little longer than the SHIPS/GFS are suggesting. Even if the shear does increase (and it should), the GFS shows it increasing from the south, which would not be as detrimental to a northward-moving disturbance as shear over 20 knots would ordinarily be.

All of the global models forecast the disturbance to not intensify beyond a marginal tropical storm, and there is even some suggestion amongst them that the system could actually start to weaken prior to landfall. While increasing shear blowing in the same direction as the storm movement is not in and of itself sufficient to incapacitate the disturbance, recall that the mountains of southern Mexico are excessively large, and when considering land interaction along with the concurrent increase in shear, the global model projections of some weakening prior to landfall is not out of the realm of realistic possibilities. Nevertheless, most of the models do forecast some short-term intensification, and even the ECMWF, while being its usual not-showing-a-tropical cyclone-self, has gotten a little more aggressive today in actually showing a broad low pressure area with the disturbance, which I didn't notice in the respective model fields yesterday.

Given this and current convective trends -- particularly the fact that the western low has all but dissipated as correctly forecast by the GFS -- I anticipate a tropical storm forming tomorrow or tomorrow night. I wouldn't be too enthusiastic about intensification potential after that, maybe up to 45 kt at the very most, with the likelihood of some weakening as the system approaches the coast on Thursday.

The system is currently wedged between an upper-level trough to the west and an upper-level ridge to the east, which is causing the system to move on an east-of-north course, toward the southern coast of Mexico. Global model guidance and UW-CIMSS steering analysis suggests this general motion should continue up until landfall. There is some difference in the models, with the ECMWF and NAVGEM showing a more prolonged northward movement which ends up being a little to the west of the landfall points for the GFS and GEM. I am inclined to blend the guidance, with a bit of a bias toward the GFS/GEM.

Regardless of development, heavy rainfall, gusty winds, and flash flooding in areas of enhanced terrain will occur by as early as tomorrow.

Probability of development in 48 hours: 60%

Probability of development in 120 hours: 60%

2014 Pacific hurricane season Invest 90E


Tropical weather analysis - May 4, 2014 - May the Fourth Be With You

By: KoritheMan, 3:54 AM GMT on May 05, 2014

Although we are still technically 11 days from the official start of the eastern north Pacific hurricane season of 2014, already there are signs of an area of disturbed weather. This disturbance has been tracked by the global model fields rather well over the last few days, and those models suggest the potential for the formation of at least a broad low pressure area. The CMC and GFS are the most aggressive, calling for the system to become a mid-range tropical storm.

Satellite images show a widespread area of cloudiness and thunderstorms stretching from roughly 115W to 95W and south of 15N to approximately 5N. The National Hurricane Center (NHC) analyzes a 1010 mb surface low within the western portion of the disturbance near 9N 111W. CIMSS vorticity and satellite data suggest that this disturbance is large and disorganized, with the 1010 mb low attempting to compete with another area of rotation to the east, near 9N 105W. While the actual surface low is officially analyzed at the more westward location for now, I am led to believe the eastern area will become the dominant feature; satellite images show a distinct area of convection in this general area, perhaps a primitive convective band, with last light low cloud lines -- complimented by the transition to nighttime shortwave infrared imagery -- also suggesting a stronger cyclonic signature within this area. Water vapor animations show cirrus emanating westward and northwestward away from the more eastern area while outflow in connection with the western area looks more restricted by the upper-level cyclonic circulation to the northwest.

Figure 1. Latest infrared satellite image of the disturbance. It hasn't been designated an invest yet, so unfortunately there is no floater. The disturbance is in the lower right corner of the image. The actual 1010 mb low analyzed by the National Hurricane Center (NHC) as of 0z is actually in the lower left portion of the disturbance. But as noted above, I anticipate the development of the eastern area more strongly given current convective trends.

The aforementioned trough appears to be retrograding northward pending the arrival of a second trough off the California coast. This should cause a temporary reduction in the already improving vertical wind shear over the area. In about 48 hours, the global models show the trough amplifying and digging southward, increasing southwesterly shear over the disturbance while also slowly lifting it northward and northeastward. In the meantime, movement of this disturbance is likely to be slow, perhaps a slow drift to the west-northwest (or north-northwest if the western low dominates). There are some differences amongst the models as to which area becomes the dominant one, with the GFS, CMC, and NOGAPS favoring formation of the eastern system, while the ECMWF is infatuated with the idea of the western low consolidating. Again, given current trends, I prefer the GFS solution. If the western low dominates, the system would likely arrive to the coast about a day or two faster. In addition, the more eastward low coalescing first would also allow the system to avoid the strongest shear and cooler waters that it would otherwise encounter along the forecast track.

I am not going to get explicit with tropical cyclone development until I see which low dominates, and how the upper-level pattern ahead of the system evolves. The models don't agree either, so I'm not just rambling unreasonably.

Regardless of development, the disturbance will spread heavy rainfall, gusty winds, and localized flooding to portions of the southern coast of Mexico by midweek. Interests there should monitor its progress, since nature is apparently oblivious to summer vacationers in the Acapulco area.

Probability of development in 48 hours: 20%

Probability of development in 120 hours: 50%

2014 Pacific hurricane season

Updated: 4:02 AM GMT on May 05, 2014


The views of the author are his/her own and do not necessarily represent the position of The Weather Company or its parent, IBM.

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Basement-dwelling pseudo-otaku with a thrill for forecasting on the side.

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