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Tropical weather analysis - August 13, 2014

By: KoritheMan , 6:38 AM GMT on August 13, 2014

Notice: All forecasts presented here are based upon my own knowledge of atmospheric dynamics. They are created using my knowledge of the various computer models, satellite interpretation, and other tools and parameters. These forecasts, while striving to be accurate, are not intended to supersede predictions by the National Hurricane Center. Always follow NWS protocol and forecasts.

Tropical Depression Eleven-E

The area of disturbed weather that has paralleled the Mexican coast over the last few days has become a tropical depression. As of the 0300Z NHC advisory, the following information was posted on the system:

Wind: 35 mph, with higher gusts
Location: 16.5°N 108.5°W
Movement: WNW at 16 mph
Pressure: 1006 mb

The depression appears to be getting better organized, and it will likely become Tropical Storm Karina in short order. Satellite data indicates the formation of curved bands to the west of the center, and a small burst of cold convection over the center proper. The outflow pattern is well-defined, with a northerly upper jet moving off the mountains of southwestern Mexico just to the east of the cyclone and enhancing the outflow in that region. In addition, the outflow appears to be excellent to the west, with the turning of the cirrus in that quadrant signifying the possibility of a large upper ridge building over the cyclone center. Earlier microwave data suggested that the center was just outside the convection on the southeast side of the thunderstorms, but recent satellite pictures indicate that it is likely under the convection now.

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

Environmental conditions appear favorable continued intensification, possibly even rapid if an inner core can become established. The SHIPS rapid intensification parameter shows a 34% chance of a 25-kt increase in winds during the next 24 hours, and I would not be surprised to see this suggestion increase with subsequent runs. My forecast is below the SHIPS but above most of the remaining intensity guidance, showing a peak of 80 kt in 96 hours. The only reason I did not go higher was because water vapor imagery shows cirrus ahead of the system along the system's trajectory from about 113W westward to about 123W, the direction of the cirrus indicating easterly to southeasterly shear. While it could be possible that this shear will get more anticyclonic with time, I am not yet convinced enough to justify a higher forecast intensity. If the shear appears less apparent tomorrow, and if current organization trends continue within the inner structure of the depression, my next forecast could show a significantly stronger cyclone. It is not out of the question at all that we could see the sixth major hurricane of the season originate from this depression, since it still has about four days over 27-28C SSTs according to areal sea surface temperature analyses; indeed, the SHIPS SST assimilation currently appears about a degree (C) too cold, a situation which has been thematic for the previous few Pacific storms. A weakening is shown after day four as the cyclone enters somewhat cooler SSTs, but with little vertical shear forecast by the GFS or ECMWF, I sense another annular hurricane may be looming. Interesting few days ahead.

The depression appears to have sped up, and may also be passing a little to the north of the 12z NHC forecast point. Water vapor imagery shows a broad mid- to upper-level trough just off the coast of California moving southeastward. The global model 500 mb height fields suggest that the cold low trailing this trough will move eastward into California over the next day or so, allowing the small weakness in the ridge to fill and propel the system on a westward track. Under the assumption that the cold low will not disappear as quickly as the models are suggesting leads me to forecast a 12-hour motion that is more toward the west-northwest. However, since the depression appears to have sped up, it is possible my forecast track could be too far north initially as the cyclone outruns the low and feels the stronger mid-level ridging found to the west of that low. After the initial west-northwest motion, a turn to the west is anticipated as the cyclone comes under a rather strong mid-level ridge. While there is general agreement on this scenario, some disparity arises in between the guidance a little later in the period, with many of the members suggesting either a turn to the southwest or a slow and erratic motion near the end of the period as the cyclone interacts with another modeled disturbance in the ITCZ to its southeast. Since this interaction appears to be getting overdone given the depth of the cyclone in both the model fields and presently, my forecast track indicates no such motion, but instead continues the generally westward motion to the south of the ridge. This forecast is north of the TVCA model consensus, and is fairly similar to the current NHC prediction, except a little faster given current motion trends.

Intensity forecast

Initial 08/13 0300Z 16.5°N 108.5°W 30 kt 35 mph
12 hour 08/13 1200Z 16.7°N 110.8°W 35 kt 40 mph
24 hour 08/14 0000Z 16.7°N 113.4°W 40 kt 45 mph
36 hour 08/14 1200Z 16.7°N 116.0°W 45 kt 50 mph
48 hour 08/15 0000Z 16.7°N 119..0°W 55 kt 65 mph
72 hour 08/16 0000Z 16.8°N 122.7°W 70 kt 80 mph
96 hour 08/17 0000Z 16.9°N 125.4°W 80 kt 90 mph
120 hour 08/18 0000Z 17.2°N 128.6°W 70 kt 80 mph

Track forecast

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


Julio has regained hurricane status as of the 0300Z CPHC advisory bulletin:

Wind: 75 mph, with higher gusts
Location: 29.4°N 158.0°W
Movement: NW at 7 mph
Pressure: 989 mb

The cloud pattern of Julio has changed little since the previous advisory. Convection has taken on less outer banding and a more prominent limitation to the broad eyewall structure. The latest SAB estimate supports the CPHC's 65 kt intensity. Interestingly, the UW-CIMSS technique appears to be running quite far behind the satellite signature, with the latest final T numbers coming in at only 2.8. Upper-tropospheric outflow is expanding to the west, heralding a decrease in southwesterly shear.

Figure 3. Latest infrared satellite image of Hurricane Julio. Image credit: NOAA's Satellite Services Division (SSD).

Despite Julio's hopefully last accolade, its nomination to hurricane status is likely to be short-lived. The models forecast a rather sharp increase in northeasterly to northerly vertical shear beginning in about 24 hours and persisting throughout the forecast period, as the broad cyclonic zone of troughiness between Alaska and Julio moves eastward in tandem with the high-latitude hurricane. The shear could easily exceed 40 kt if the GFS and ECMWF are correct, which will be extremely prohibitive to a northeastward-moving system. Actually, it is entirely possible Julio could weaken faster than I've suggested below, but most of the guidance still hangs onto the system for at least the next four days, but they could of course be underestimating the deleterious effect of the shear. I would also like to see if the high shear values seen on the GFS/ECMWF fields verifies before I decide to terminate Julio too quickly. It is possible my next forecast will have to show a quicker demise.

Julio appears to be moving northwest, and is following the current CPHC prediction rather behaviorally. There is far less spread in the guidance than there has been, although there is still some differences on the sharpness and onset of recurvature. The ECMWF is to the left of the GFS and shows Julio moving northward as it slowly decays, whlie the GFDL and HWRF show a similar trajectory to the GFS, but ended up slower and farther south, instead showing a sheared system stalling south of 35N. This is likely in response to the anticipated shear, and I have actually blended this solution into my forecast at the end of the period, as I feel it is a viable one; strong shear can often retard speedy movement in the direction of the shear, and that is what I have shown below, with Julio likely to move slowly northward between 72 and 96 hours as it begins to feel the shear, and is also steered by a low- to mid-level ridge to the east. This forecast is not too dissimilar to the current CPHC prediction, and favors the GFS solution over the ECMWF, as that model has been handling this hurricane well for days.

Intensity forecast

Initial 08/13 0300Z 29.4°N 158.0°W 65 kt 75 mph
12 hour 08/13 1200Z 30.0°N 158.6°W 65 kt 75 mph
24 hour 08/14 0000Z 30.5°N 158.7°W 60 kt 70 mph
36 hour 08/14 1200Z 31.3°N 158.4°W 50 kt 60 mph
48 hour 08/15 0000Z 32.4°N 157.5°W 45 kt 50 mph
72 hour 08/16 0000Z 33.4°N 156.6°W 35 kt 40 mph
96 hour 08/17 0000Z 34.0°N 156.6°W 30 kt: post-tropical/remmant low
120 hour 08/18 0000Z: dissipated

Track forecast

Figure 4. My forecast track for Julio.

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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2. WunderAlertBot (Admin)
6:23 AM GMT on August 16, 2014
KoritheMan has created a new entry.
1. Astrometeor
7:15 PM GMT on August 13, 2014
Okay, initial projected peak is 90. Let's see how high she goes.
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Basement-dwelling pseudo-otaku with a thrill for forecasting on the side.

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