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Tropical weather analysis - August 9, 2014

By: KoritheMan , 6:04 AM GMT on August 09, 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.


Julio continues moving across the central Pacific as a hurricane. As of the 0300Z CPHC advisory bulletin, the following coordinates were given on the hurricane:

Wind: 100 mph, with higher gusts
Location: 18.9°N 144.7°W
Movement: WNW at 16 mph
Pressure: 970 mb
Category: 2 (Saffir-Simpson Hurricane Wind Scale)

Satellite imagery shows that Julio continues to slowly weaken over cool water, with the latest SHIPS file showing an approximate SST value of 25.4C. That file, along with other regional sea surface temperature analyses, indicates that those waters are the coldest Julio will encounter along the forecast track, but for now they're certainly doing their job expediently. A recently-received 343Z SSMIS microwave pass, however, still shows a formidable eastern eyewall, with the eye apparently open to the west. Upper-tropospheric outflow continues to be relatively well-defined, implying a continued environment of weak vertical wind shear.

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

The intensity forecast for Julio may prove a bit difficult. On one hand, as previously mentioned, the hurricane is now moving across the coldest waters it will encounter along the forecast track. While the waters only gradually warm, any additional input of heat will provide a tropical cyclone with enormous amounts of energy. However, water vapor imagery shows upper-level cirrus debris blowing southwest to northeast not far to the west of Julio, suggesting that wind shear may increase over the hurricane sooner rather than later. Indeed, looking at the models runs this evening, it is apparent that both the GFS and ECMWF foresee an increase in southwesterly shear beginning in around 36 hours. Given current trends on water vapor imagery, I hold that forecast with the utmost predilection. By day four, the models show shear relaxing, and even though the limitations of the map I create my forecast tracks on doesn't allow me to indicate a forecast point beyond 72 hours, an abrupt halt to the expected weakening appears likely at that time, especially since waters warm to around 27C to the north of the Hawaiian Islands. Also, while I'm not explicitly anticipating it at this time, it is possible that some restrengthening could occur at longer ranges as the shear abates and the waters warm, a scenario which is now supported by some of the intensity guidance.

While Julio has been moving generally toward the west-northwest, recent satellite data suggests more of a jog to the north-northwest. This is assumed to be a temporary motion, with model data and real-time synoptic observations still supporting a continued west-northwestward motion over the next several days. While there exists some notable disagreements on the approximate latitude at which Julio will turn, all of the global and dynamical models show the cyclone bending to the left after about 72 hours, with the ECMWF showing a sharper westward turn than the GFS. Overall, the guidance remains in good agreement on Julio passing well north of the Hawaiian Islands, and the southern fringes of the cone of uncertainty no longer lies over the state. Until that turn becomes more definite, however, interests there should continue to carefully assess future forecasts on Julio. On the current track, Julio's rains and winds will miss the islands, but it will cause a disruption of the normally uniform trade wind flow, and could also generate some high surf.

Intensity forecast

Initial 08/09 0300Z 18.9°N 144.7°W 85 kt 100 mph
12 hour 08/09 1200Z 19.9°N 146.9°W 80 kt 90 mph
24 hour 08/10 0000Z 21.1°N 149.7°W 75 kt 85 mph
36 hour 08/10 1200Z 22.4°N 151.8°W 65 kt 75 mph
48 hour 08/11 0000Z 23.7°N 154.7°W 60 kt 70 mph
72 hour 08/12 0000Z 25.4°N 157.7°W 50 kt 60 mph

Track forecast

Figure 2. 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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6:56 AM GMT on August 11, 2014
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Basement-dwelling pseudo-otaku with a thrill for forecasting on the side.

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