Tropical Storm Julio

Tropical Storm Julio Track 0300 Hours September 7 2020
Tropical Storm Julio Track 0300 Hours September 7 2020

Tropical Storm Julio Wind Speed FieldTropical Storm Julio – NWS National Hurricane Center Miami FL 300 AM MDT Mon Sep 07, 2020 (see video below)

Moderate easterly shear has continued to take a toll on the compact tropical cyclone. In fact, recent satellite imagery and ASCAT data indicate that the small circulation has opened up into a trough of  low pressure. Therefore, Julio has dissipated and this will be the final NHC advisory on this system. Julios demise occurred much quicker than forecast, owing to the difficulty in predicting the intensity (both up and down) of small tropical cyclones. The remnants are moving westward around the northern portion of a broad area of low pressure to the southwest of Socorro Island, and the remnants should be absorbed within that system later today. The global models indicate that moderate to strong easterly shear will persist over the larger low pressure area in which Julio is being absorbed, and this will likely prevent significant development of that system over the next few days.

This is last NHC advisory on this system.

FORECAST POSITIONS AND MAX WINDS

INIT  07/0900Z 19.5N 112.6W   25 KT  30 MPH - Low (WSW Puerto Vallarta, Mexico)
 12H  07/1800Z...DISSIPATED

NWS National Hurricane Center Miami FL 300 PM MDT Sun Sep 06, 2020 

Julio remains a compact tropical storm that is producing a small area of deep convection near and to the west of the center. A recent ASCAT-A overpass showed maximum winds around 30 kt, which was lower than in previous passes. Based on that data and the latest Dvorak classifications, the initial intensity is lowered to 35 kt. The ASCAT data also suggest that the circulation of Julio is not as well defined on the south side as it was earlier.

As mentioned in the previous discussion, Julio’s future is somewhat unclear. The ECMWF and UKMET models show Julio becoming absorbed by a larger low just to its southwest in a couple of days. Conversely, the GFS, HWRF, and HMON models show Julio being the dominant feature, with the latter two aids even showing strengthening. Since confidence is low on which scenario will play out, it seems best to hold continuity for now, which ends up leaning closer to the ECMWF/UKMET solutions. The NHC intensity forecast is a little lower than the previous one given the lower initial intensity.

The tropical storm is moving west-northwestward at about 17 kt. Julio should continue to move westward to west-northwestward at a fairly quick pace for another 12-24 hours. However, after that time, a notable slow down should occur as the ridge over the eastern Pacific breaks down and leaves the cyclone in weak steering currents. The new NHC track forecast is adjusted to the south of the previous one to come into better agreement with the latest models.

FORECAST POSITIONS AND MAX WINDS

INIT  06/2100Z 19.3N 110.0W   35 KT  40 MPH - Tropical Storm (WSW Puerto Vallarta, Mexico)
 12H  07/0600Z 19.6N 112.3W   40 KT  45 MPH - Tropical Storm (WSW Puerto Vallarta, Mexico)
 24H  07/1800Z 19.7N 114.2W   40 KT  45 MPH - Tropical Storm (WSW Puerto Vallarta, Mexico)
 36H  08/0600Z 19.6N 115.4W   40 KT  45 MPH - Tropical Storm (WSW Puerto Vallarta, Mexico)
 48H  08/1800Z 19.4N 116.1W   35 KT  40 MPH - Tropical Storm (WSW Puerto Vallarta, Mexico)
 60H  09/0600Z 19.2N 116.7W   35 KT  40 MPH - Depression (WSW Puerto Vallarta, Mexico)
 72H  09/1800Z...DISSIPATED

NWS National Hurricane Center Miami FL 900 AM MDT Sun Sep 06, 2020 

Julio has surprisingly accelerated west-northwestward during the past few hours, moving around the northeast periphery of a broad trough of low pressure. The tiny tropical storm continues to produce small but frequent bursts of central convection and has not changed appreciably since the most recent ASCAT pass that supported an intensity of 40 kt.

Julio’s future is unusually unclear for a system that is forecast to dissipate. The global models are struggling to resolve Julio, and only the ECMWF has a realistic current depiction of the cyclone. Those models universally indicate that Julio will either dissipate or be absorbed by the aforementioned broad area of low pressure located to its southwest within the next 24 to 36 hours. This is certainly plausible given Julio’s small size and limited convection. On the other hand, the HWRF and HMON models now indicate that Julio will not only persist through day 5, but potentially strengthen when upper-level winds are forecast to become less hostile in a couple days. The disagreement can not be explained entirely by model resolution as the COAMPS-TC also weakens Julio.

I see no clear reason to support one solution over another at this point. Therefore, the official forecast continues to show dissipation for now, though the intensity has been hedged slightly higher at 48 h and 60 h. The NHC track forecast leans heavily on the HWRF and HMON models and has been adjusted significantly faster for the first 24 h due to Julio’s recent acceleration. Much larger changes may be required to the forecast later today or tonight if it becomes more likely that Julio will persist longer than currently indicated.

FORECAST POSITIONS AND MAX WINDS

INIT  06/1500Z 19.2N 108.8W   40 KT  45 MPH - Tropical Storm (WSW Puerto Vallarta, Mexico)
 12H  07/0000Z 19.9N 111.1W   45 KT  50 MPH - Tropical Storm (WSW Puerto Vallarta, Mexico)
 24H  07/1200Z 20.3N 113.6W   45 KT  50 MPH - Tropical Storm (WSW Puerto Vallarta, Mexico)
 36H  08/0000Z 20.4N 115.1W   45 KT  50 MPH - Tropical Storm (WSW Puerto Vallarta, Mexico)
 48H  08/1200Z 20.2N 115.9W   40 KT  45 MPH - Tropical Storm (WSW Puerto Vallarta, Mexico)
 60H  09/0000Z 20.2N 116.8W   35 KT  40 MPH - Depression (WSW Puerto Vallarta, Mexico)
 72H  09/1200Z...DISSIPATED

NWS National Hurricane Center Miami FL 1000 PM CDT Sat Sep 05, 2020 

Satellite imagery, including recently received microwave overpasses, shows that Julio has changed little in organization during the past several hours, with the small low-level circulation center is located near the eastern edge of the small area of central convection. The initial intensity remains 35 kt based on continuity and a satellite intensity estimated from TAFB.

The initial motion is west-northwestward or 295/15 kt. The latest global models runs continue to have trouble resolving Julio, but overall the cyclone is embedded in an east-southeasterly flow on the southwest side of a mid-level ridge. A general west- northwestward motion should continue with a decrease in forward speed until the system dissipates. The new forecast track again leans more toward the ECMWF model, which does the best job of resolving Julio.

The tropical storm will be affected by moderate to strong easterly wind shear for the next day or two, and only sight strengthening is likely during that time. While the shear is forecast to diminish after 24-36 h, the cyclone will encounter a drier and more stable air mass at that time, which should lead to the dissipation of the small system. The new intensity forecast is unchanged from the previous forecast, and it lies below the intensity consensus.

FORECAST POSITIONS AND MAX WINDS

INIT  06/0300Z 16.6N 104.2W   35 KT  40 MPH - Tropical Storm (WNW Acapulco, Mexico)
 12H  06/1200Z 17.5N 106.4W   40 KT  45 MPH - Tropical Storm (WSW Petalan, Mexico)
 24H  07/0000Z 18.5N 108.7W   40 KT  45 MPH - Tropical Storm (WSW Manzanillo, Mexico)
 36H  07/1200Z 19.4N 110.1W   35 KT  40 MPH - Tropical Storm (WSW Manzanillo, Mexico)
 48H  08/0000Z 20.3N 110.8W   30 KT  35 MPH - Depression (WSW Puerto Vallarta, Mexico)
 60H  08/1200Z 21.1N 111.2W   20 KT  25 MPH - Low (WSW Cabo San Lucas, Mexico)
 72H  09/0000Z...DISSIPATED

NWS National Hurricane Center Miami FL 400 PM CDT Sat Sep 05, 2020

The mid-level remnants of Atlantic Hurricane Nana have moved westward and west-northwestward off the southwestern coast of Mexico while producing intermittent convection during the last few days. A well-defined low formed about a day ago and ASCAT data indicates that it has been producing tropical-storm-force winds for the past 12 h or so. During the past few hours there has also been an increase in deep convection near the center of the low, and the most recent Dvorak classification from TAFB was T-2.5, indicating that the system is sufficiently well-organized to be considered a tropical cyclone. Since the low-level center of Nana dissipated inland over Central Atlantic, the new tropical storm is named Julio, the tenth of the northern East Pacific season. The TAFB Dvorak classification and 15Z ASCAT data are the basis for the 35 kt initial intensity. Since the ASCAT explicitly showed 35 kt winds and that instrument typically under-samples the maximum winds, it is possible this intensity is a little conservative.

Most of the dynamical models do not acknowledge the existence of tiny Julio in their initial conditions. Only the ECMWF and its ensemble show a small well-defined low and it therefore is the primary basis for the NHC track forecast. In general, Julio should continue west-northwestward at a slower forward speed for the next couple of days, steered by a mid-level ridge to the northeast. Julio is forecast to become a shallow remnant low in a few days and should slow down to a crawl before it dissipates early next week. Since the forecast is based largely on one modeling system rather than the typical NHC consensus approach, confidence in the track forecast is fairly low.

The tropical storm will be affected by strong easterly wind shear for the next day or two and little or no further strengthening is likely during that time. Although the shear could decrease by early next week, Julio will reach a drier and more stable environment in a couple of days. It is therefore forecast to become a remnant low within 60 h and dissipate shortly thereafter. The NHC forecast is based on a blend of the ECMWF and the statistical DSHP and LGEM models since the HWRF and the GFS-dependent HMON models do not appear to have a good handle on the initial state of the system.

FORECAST POSITIONS AND MAX WINDS

INIT  05/2100Z 16.1N 102.7W   35 KT  40 MPH - Tropical Storm (WNW Acapulco, Mexico)
 12H  06/0600Z 16.9N 105.0W   40 KT  45 MPH - Tropical Storm (WSW Petalan, Mexico)
 24H  06/1800Z 18.0N 107.5W   40 KT  45 MPH - Tropical Storm (WSW Manzanillo, Mexico)
 36H  07/0600Z 19.0N 109.4W   35 KT  40 MPH - Tropical Storm (WNW Manzanillo, Mexico)
 48H  07/1800Z 19.9N 110.6W   30 KT  35 MPH - Depression (WSW Puerto Vallarta, Mexico)
 60H  08/0600Z 20.5N 111.0W   25 KT  30 MPH - Low (WSW Cabo San Lucas, Mexico)
 72H  08/1800Z...DISSIPATED

NWS National Hurricane Center Miami FL 1100 AM PDT Thu Sep 3, 2020

For the eastern North Pacific…east of 140 degrees west longitude:

  • 1. The remnants of Atlantic basin Tropical Storm Nana, are expected to emerge over the extreme eastern Pacific waters near the Gulf of Tehuantepec on Friday. Unfavorable upper-level winds are expected to inhibit significant development through early next week while the system moves generally west-northwestward, near or along the southern coast of Mexico. * Formation chance through 48 hours…low…10 percent. * Formation chance through 5 days…low…20 percent.

If this system is named, it will become Tropical Storm Julio.

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