Tropical Storm Polo

Tropical Depression Polo Track 0700 Hours November 19 2020
Tropical Depression Polo Track 0700 Hours November 19 2020

Tropical Storm Polo Wind Speed FieldTropical Storm Polo – NWS National Hurricane Center Miami FL 700 AM PST Thu Nov 19, 2020

Occasional bursts of deep convection have been developing to the east and northeast of Polo’s center since yesterday evening, but none have lasted for more than about an hour or two. ASCAT-C data received after the scatterometer pass noted in the previous advisory did not explicitly show tropical-storm-force winds, suggesting that Polo continues to weaken, and the most recent Dvorak CI numbers from TAFB and SAB are 2.0. For these reasons, Polo is now assumed to be a 30-kt tropical depression. Polo has not maintained enough organized convection to be considered a tropical cyclone for the last 12 to 15 hours, and if sustained convection does not redevelop soon, the system will likely be declared a remnant low later this afternoon. The remnant low is expected to continue weakening due to westerly shear, only marginally warm waters, and dry air, and it is expected to dissipate by 48 hours, if not sooner.

Polo is being steered westward (275/10 kt) to the south of a low- to mid-level ridge. Once Polo becomes a remnant low, the shallow circulation should take on a south-of-due-west motion in about 24 hours, continuing that trajectory until it dissipates. This pattern is shown by nearly all the reliable track models, and the NHC forecast lies down the middle of the guidance envelope.

FORECAST POSITIONS AND MAX WINDS

INIT  19/1500Z 17.1N 120.3W   30 KT  35 MPH - Depression (WSW Acapulco, Mexico)
 12H  20/0000Z 17.1N 121.8W   25 KT  30 MPH - Low (WSW Acapulco, Mexico)
 24H  20/1200Z 17.0N 123.8W   25 KT  30 MPH - Low (WSW Acapulco, Mexico)
 36H  21/0000Z 16.7N 126.2W   20 KT  25 MPH - Low (WSW Acapulco, Mexico)
 48H  21/1200Z...DISSIPATED

NWS National Hurricane Center Miami FL 700 AM PST Wed Nov 18, 2020

Satellite images indicate that the depression has strengthened into a tropical storm. The small central dense overcast has grown during the past several hours and a few banding features have formed. Dvorak estimates range from 30 to 45 kt, and the initial wind speed is set to 40 kt, which matches the latest CIMSS satellite consensus estimate. Polo could strengthen a little more today, but an increase in shear and dry-air entrainment should start the weakening process on Thursday, with the system expected to become a non-convective remnant low on Friday. The new NHC forecast is a little below the model consensus, close to the previous NHC forecast, leaning toward the idea that the small tropical cyclone will probably weaken faster than the bulk of the guidance anticipates.

The initial motion continues to be west-northwestward at 10 kt. There has been no change to the forecast philosophy, with Polo forecast to remain on the southern side of a mid-level ridge throughout the period. The storm should turn more westward on Thursday as the system weakens and becomes more shallow. The new forecast is south of the latest model consensus, nudged slightly north of the previous NHC forecast.

FORECAST POSITIONS AND MAX WINDS

INIT  18/1500Z 16.3N 116.0W   40 KT  45 MPH - Tropical Storm (WSW Acapulco, Mexico)
 12H  19/0000Z 16.5N 117.6W   40 KT  45 MPH - Tropical Storm (WSW Acapulco, Mexico)
 24H  19/1200Z 16.7N 119.6W   35 KT  40 MPH - Tropical Storm (WSW Acapulco, Mexico)
 36H  20/0000Z 16.9N 121.5W   30 KT  35 MPH - Depression (WSW Acapulco, Mexico)
 48H  20/1200Z 17.0N 123.6W   25 KT  30 MPH - Low (WSW Acapulco, Mexico)
 60H  21/0000Z 17.0N 126.0W   25 KT  30 MPH - Low (WSW Acapulco, Mexico)

NWS National Hurricane Center Miami FL 800 PM MST Tue Nov 17, 2020

Conventional satellite imagery and an earlier AMSR2 microwave pass showed curved bands developing over the western portion of the cyclone, although deep convection remains rather limited near the depression’s surface center. Subjective satellite intensity estimate T-numbers haven’t changed during the past 6 hours and the initial intensity is held at 30 kt for this advisory.

The HCCA and IVCN multi-model intensity aids along with the LGEM model indicate that the depression will strengthen to a low-end tropical storm during the next 12-24 hrs and the NHC forecast continues to show this trend. Afterward, modest west-southwesterly shear, cooler oceanic temperatures, and the presence of a very dry and stable air mass should cause the cyclone to weaken and degenerate to a remnant low in 2 days. The deterministic guidance agrees that the depression will open up into a trough of low pressure in 4 days, or less. This is also reflected in the official intensity forecast.

The initial motion is estimated to be west-northwestward, or 285/10 kt in the mid-tropospheric steering current provided by high pressure anchored to the north of the cyclone. The depression is expected to continue in this general motion through Thursday. Through the remaining forecast period, the depression is forecast to turn westward in the low-level easterly flow as a shallow, or vertically limited cyclone. The track forecast is basically an update of the previous one and is close to the HCCA and TVCE consensus models.

FORECAST POSITIONS AND MAX WINDS

INIT  18/0300Z 15.5N 114.3W   30 KT  35 MPH - Depression (WSW Acapulco, Mexico)
 12H  18/1200Z 15.9N 115.9W   35 KT  40 MPH - Tropical Storm (WSW Acapulco, Mexico)
 24H  19/0000Z 16.5N 118.0W   35 KT  40 MPH - Tropical Storm (WSW Acapulco, Mexico)
 36H  19/1200Z 16.9N 120.0W   30 KT  35 MPH - Depression (WSW Acapulco, Mexico)
 48H  20/0000Z 17.3N 122.1W   25 KT  30 MPH - Low (WSW Acapulco, Mexico)
 60H  20/1200Z 17.3N 124.3W   25 KT  30 MPH - Low (WSW Acapulco, Mexico)
 72H  21/0000Z...DISSIPATED

NWS National Hurricane Center Miami FL 200 PM MST Tue Nov 17, 2020

Corrected Daylight Time to Standard time

Visible satellite imagery and recent ASCAT data indicate that the circulation of the area of low pressure located well south-southwest of Baja California has become better defined today. The associated convective activity has also become organized in a band around the western and southwestern portions of the circulation. Therefore, the system is being classified as a tropical depression with winds of 30 kt, as indicated by the scatterometer data and a T2.0 (30 kt) Dvorak classification from TAFB.

The depression is currently located over SSTs of around 28 deg C, and within a low shear environment. These conditions are conducive for strengthening, but the surrounding mid-level environment is fairly dry which is likely to limit intensification. Most of the intensity guidance calls for the system to become a short-lived tropical storm, and so does the official forecast. After 24 hours, increasing upper-level westerly winds, cooler SSTs, and even less favorable thermodynamic conditions should cause the cyclone to weaken. The system is likely to become a remnant low in about 48 hours, and the global models show it degenerating into a trough of low pressure in 60-72 hours, which is also indicated in the NHC forecast.

The initial motion estimate is 285/11 kt. A mid-level ridge that extends westward from northern Mexico over the eastern Pacific should steer the system west-northwestward for the next couple of days. After that time, the cyclone is likely to turn more westward as it weakens and is steered by the low-level trade wind flow. The track guidance is in good agreement, and the NHC forecast is near the middle of the guidance envelope.

FORECAST POSITIONS AND MAX WINDS

INIT  17/2100Z 15.2N 113.3W   30 KT  35 MPH - Depression (WSW Acapulco, Mexico)
 12H  18/0600Z 15.6N 114.9W   35 KT  40 MPH - Tropical Storm (WSW Acapulco, Mexico)
 24H  18/1800Z 16.2N 117.0W   35 KT  40 MPH - Tropical Srtorm (WSW Acapulco, Mexico)
 36H  19/0600Z 16.7N 119.1W   30 KT  35 MPH - Depression (WSW Acapulco, Mexico)
 48H  19/1800Z 17.1N 121.1W   25 KT  30 MPH - Low (WNW Acapulco, Mexico)
 60H  20/0600Z 17.2N 123.3W   20 KT  25 MPH - Low (WNW Acapulco, Mexico)
 72H  20/1800Z...DISSIPATED

NWS National Hurricane Center Miami FL 400 AM PST Tue Nov 17, 2020

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

  • 1. Showers and thunderstorms associated with a broad area of low pressure located several hundred miles southwest of the coast of southwestern Mexico have changed little in organization overnight. Although environmental conditions are only somewhat conducive for development, a short-lived tropical depression could still form within a day or so as the system moves west-northwestward or northwestward at about 10 mph. Conditions are forecast to become increasingly unfavorable for further development on Thursday. * Formation chance through 48 hours…medium…50 percent. * Formation chance through 5 days…medium…50 percent.

NWS National Hurricane Center Miami FL 400 PM PST Mon Nov 16, 2020

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

  • 1. Showers and thunderstorms continue to become better organized in association with a broad area of low pressure located several hundred miles southwest of the coast of southern Mexico. Although environmental conditions are only somewhat conducive for development, a short-lived tropical depression could still form within the next couple of days as the low moves west-northwestward or northwestward at about 10 mph, away from the coast of Mexico. By midweek, conditions are forecast to become increasingly unfavorable for further development. * Formation chance through 48 hours…medium…50 percent. * Formation chance through 5 days…medium...50 percent.

NWS National Hurricane Center Miami FL 1000 AM PST Mon Nov 16, 2020

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

  • 1. Showers and thunderstorms associated with a broad area of low pressure located several hundred miles southwest of the coast of southern Mexico have increased and become a little better organized since yesterday. Although environmental conditions are forecast to be only marginally conducive, some additional development is possible, and the system could become a short-lived tropical depression within the next couple of days. The low is forecast to move west-northwestward or northwestward at about 10 mph away from the coast of Mexico. Conditions are expected to become unfavorable for further development around midweek. * Formation chance through 48 hours…medium…40 percent. * Formation chance through 5 days…medium...40 percent.

NWS National Hurricane Center Miami FL 400 PM PST Sun Nov 15, 2020

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

  • 1. Satellite imagery indicates that showers and thunderstorms remain displaced well to the southeast of a broad area of low pressure located several hundred miles southwest of the coast of southern Mexico. Environmental conditions are expected to remain marginally conducive for development over the next couple of days or so as the system moves slowly west-northwestward or northwestward away from the coast of Mexico. Thereafter, conditions are forecast to become unfavorable for further development by the middle of this week. * Formation chance through 48 hours…low…20 percent. * Formation chance through 5 days…low…30 percent.

NWS National Hurricane Center Miami FL 400 AM PST Sun Nov 15, 2020

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

  • 1. Shower and thunderstorm activity associated with a broad area of low pressure located several hundred miles southwest of the coast of southern Mexico has increased somewhat overnight. Although environmental conditions are only marginally favorable, some slow development of this system is possible, and a tropical depression could form within a few days as the system moves slowly west-northwestward or northwestward away from the coast of Mexico. By mid week, conditions are expected to become unfavorable for further development. * Formation chance through 48 hours…low…30 percent. * Formation chance through 5 days…medium…40 percent.

NWS National Hurricane Center Miami FL 400 PM PST Sat Nov 14, 2020

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

  • 1. A broad and disorganized area of low pressure located several hundred miles southwest of the coast of southern Mexico is producing limited shower activity. Environmental conditions are still forecast to be somewhat conducive for gradual development, and a tropical depression could form early next week as the system moves slowly west-northwestward or northwestward away from the coast of Mexico. By late next week, conditions are expected to become unfavorable for further development. * Formation chance through 48 hours…medium…40 percent. * Formation chance through 5 days…medium...60 percent.

NWS National Hurricane Center Miami FL 1000 AM PST Sat Nov 14, 2020

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

  • 1. Shower and thunderstorm activity remains disorganized in association with a broad area of low pressure located several hundred miles southwest of the coast of southern Mexico. However, environmental conditions appear conducive for gradual development, and a tropical depression is likely to form early next week as the system moves slowly west-northwestward or northwestward away from the coast of Mexico. By late next week, conditions are expected to become unfavorable for further development. * Formation chance through 48 hours…medium…50 percent. * Formation chance through 5 days…high…70 percent.

NWS National Hurricane Center Miami FL 400 AM PST Sat Nov 14, 2020

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

  • 1. Shower and thunderstorm activity has changed little in organization overnight in association with a broad area of low pressure located several hundred miles southwest of the coast of southern Mexico. Environmental conditions appear conducive for gradual development, and a tropical depression is likely to form late this weekend or early next week as the system moves slowly west-northwestward or northwestward away from the coast of Mexico. * Formation chance through 48 hours…medium…50 percent. * Formation chance through 5 days…high…70 percent.

NWS National Hurricane Center Miami FL 400 PM PST Fri Nov 13, 2020

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

  • 1. Showers and thunderstorms continue to increase in coverage and organization near a broad area of low pressure located several hundred miles southwest of the coast of southern Mexico. Environmental conditions are expected to be conducive for gradual development, and a tropical depression is likely to form late this weekend or early next week as the system moves slowly west-northwestward or northwestward away from the coast of Mexico. * Formation chance through 48 hours…medium…50 percent. * Formation chance through 5 days…high...70 percent.

NWS National Hurricane Center Miami FL 1000 AM PST Fri Nov 13, 2020

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

  • 1. Showers and thunderstorms have increased this morning in association with an area of low pressure located several hundred miles southwest of the coast of Mexico. Environmental conditions are forecast to be conducive for some gradual development, and a tropical depression is likely to form late this weekend or early next week as the system moves slowly toward the west-northwest away from the coast of Mexico. * Formation chance through 48 hours…medium…40 percent. * Formation chance through 5 days…high…70 percent.

NWS National Hurricane Center Miami FL 400 AM PST Fri Nov 13, 2020

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

  • 1. An area of low pressure located several hundred miles southwest of the coast of Mexico is producing disorganized showers and thunderstorms. Environmental conditions are forecast to be conducive for some gradual development, and a tropical depression could form during the early-to-middle portion of next week as the system moves slowly toward the west-northwest away from the coast of Mexico. * Formation chance through 48 hours…low…30 percent. * Formation chance through 5 days…medium…60 percent.

NWS National Hurricane Center Miami FL 1000 PM PST Thu Nov 12 2020

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

  • 1. An area of low pressure located several hundred miles southwest of the coast of Mexico is producing disorganized showers and thunderstorms. Environmental conditions are forecast to be marginally conducive for development, and a tropical depression could form by mid next week as the system moves slowly toward the west-northwest over the open eastern Pacific. * Formation chance through 48 hours…low…20 percent. * Formation chance through 5 days…medium…60 percent.

NWS National Hurricane Center Miami FL 400 PM PST Thu Nov 12, 2020

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

  • 1. An area of low pressure has formed several hundred miles southwest of the coast of Mexico. Environmental conditions are forecast to be generally favorable for gradual development, and a tropical depression could form early next week as the system drifts slowly west-northwestward over the eastern Pacific. * Formation chance through 48 hours…low…20 percent. * Formation chance through 5 days…medium…60 percent.

NWS National Hurricane Center Miami FL 1000 AM PST Thu Nov 12, 2020

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

  • 1. A broad area of low pressure is expected to form several hundred miles southwest of the coast of Mexico this weekend. Environmental conditions are forecast to be generally favorable for gradual development, and a tropical depression could form early next week as the system drifts slowly west-northwestward over the eastern Pacific. * Formation chance through 48 hours…low…0 percent. * Formation chance through 5 days…medium…50 percent.

NWS National Hurricane Center Miami FL 400 AM PST Thu Nov 12 2020

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

  • 1. A broad area of low pressure is expected to form several hundred miles southwest of the coast of Mexico this weekend. Environmental conditions are forecast to be generally favorable for gradual development, and a tropical depression could form early next week as the system drifts slowly west-northwestward over the eastern Pacific. * Formation chance through 48 hours…low…0 percent. * Formation chance through 5 days…medium…40 percent.

NWS National Hurricane Center Miami FL 1000 PM PST Wed Nov 11, 2020

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

  • 1. A broad area of low pressure is expected to form several hundred miles southwest of the coast of Mexico late this week. Environmental conditions are forecast to be generally favorable for slow development through the weekend and early next week as the system drifts slowly west-northwestward over the eastern Pacific. * Formation chance through 48 hours…low…0 percent. * Formation chance through 5 days…low...30 percent.

NWS National Hurricane Center Miami FL 400 PM PST Wed Nov 11 2020

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

  • 1. A broad area of low pressure is expected to form several hundred miles southwest of the coast of Mexico late this week. Environmental conditions are forecast to be generally favorable for slow development through the weekend and early next week as the system drifts slowly west-northwestward over the eastern Pacific. * Formation chance through 48 hours…low…0 percent. * Formation chance through 5 days…low…30 percent.

NWS National Hurricane Center Miami FL 1000 AM PST Wed Nov 11, 2020

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

  • 1. A broad area of low pressure could form several hundred miles southwest of the coast of Mexico late this week. Environmental conditions are forecast to be generally favorable for slow development through the weekend and early next week as this system drifts slowly west-northwestward over the eastern Pacific. * Formation chance through 48 hours…low…0 percent. * Formation chance through 5 days…low…30 percent.

NWS National Hurricane Center Miami FL 400 AM PST Wed Nov 11, 2020

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

  • 1. A broad area of low pressure could form several hundred miles southwest of the coast of Mexico late this week. Environmental conditions are forecast to be generally favorable for slow development through the weekend and early next week as this system drifts slowly west-northwestward over the east Pacific. * Formation chance through 48 hours…low…0 percent. * Formation chance through 5 days…low...20 percent.

If this storm system is named, it will be named Tropical Storm Polo.

Article Resources:

Recent Tropical Cruise Weather: