Tropical Storm Octave

Post Tropical Storm Octave Track 1400 Hours October 19 2019
Post Tropical Storm Octave Track 1400 Hours October 19 2019

Tropical Storm Octave Forming Satellite 1400 Hours October 17, 2019

Tropical Storm Octave – NWS National Hurricane Center Miami FL 200 PM PDT Sat Oct 19, 2019

Deep convection has not returned, now being absent for at least 12 hours. The environment around Octave is dry and stable, and it is unlikely that significant convection will come back any time soon. Octave has therefore become a remnant low, and its maximum winds are estimated to be 30 kt based on recent scatterometer data. The remnant low is expected to linger for at least the next 5 days with its intensity holding steady or decreasing due to moderate southeasterly shear and mid-level relative humidities of 30-40 percent.

The initial motion remains very slowly east-northeastward, or 070/2 kt. The remnant low is trapped in a weak steering regime, and it is expected to meander for the next 5 days, only moving a net distance of 50-100 n mi during that period. A slight westward adjustment was made to this last NHC official forecast to account for the latest multi-model consensus aids and the ECMWF, which lies along the western edge of the guidance envelope.

FORECAST POSITIONS AND MAX WINDS

INIT  19/2100Z 11.6N 125.7W   30 KT  35 MPH - (ESE Hilo, Hawaii)
 12H  20/0600Z 11.4N 125.7W   25 KT  30 MPH - (ESE Hilo, Hawaii)
 24H  20/1800Z 11.1N 125.7W   25 KT  30 MPH - (ESE Hilo, Hawaii)
 36H  21/0600Z 10.8N 125.7W   25 KT  30 MPH - (ESE Hilo, Hawaii)
 48H  21/1800Z 10.9N 125.7W   25 KT  30 MPH - (ESE Hilo, Hawaii)
 72H  22/1800Z 11.7N 125.8W   25 KT  30 MPH - (ESE Hilo, Hawaii)
 96H  23/1800Z 12.4N 125.4W   20 KT  25 MPH - (ESE Hilo, Hawaii)
120H  24/1800Z 12.0N 124.6W   20 KT  25 MPH - (ESE Hilo, Hawaii)

NWS National Hurricane Center Miami FL 800 AM PDT Sat Oct 19, 2019

Octave’s last bit of deep convection dissipated about 6 hours ago, around 0900 UTC, leaving the cyclone as a swirl of low-level clouds. The maximum winds are still estimated to be 30 kt based mainly on the CI number from TAFB. Octave could still produce intermittent bursts of convection during the next several days, but increased shear and a dry air mass with mid-level relative humidities of 30-40 percent are likely to keep the activity from being persistent or well organized. If deep convection doesn’t redevelop soon, then Octave would be declared a remnant low later today. The cyclone’s maximum winds should decrease a little more in the short term, but the remnant low is likely to persist near the Intertropical Convergence Zone for the entire 5-day forecast period.

Octave is moving slowly east-northeastward, or 070/2 kt. The depression is caught in a weak steering pattern, and it is likely to meander around for the next 5 days, never reaching speeds any higher than about 3 kt. No significant changes to the NHC track forecast were made from the previous advisory.

FORECAST POSITIONS AND MAX WINDS

INIT  19/1500Z 11.5N 125.9W   30 KT  35 MPH - Tropical Depression (ESE Hilo, Hawaii)
 12H  20/0000Z 11.6N 125.6W   25 KT  30 MPH - Low (ESE Hilo, Hawaii)
 24H  20/1200Z 11.3N 125.5W   25 KT  30 MPH - Low (ESE Hilo, Hawaii)
 36H  21/0000Z 10.9N 125.5W   25 KT  30 MPH - Low (ESE Hilo, Hawaii)
 48H  21/1200Z 10.8N 125.5W   25 KT  30 MPH - Low (ESE Hilo, Hawaii)
 72H  22/1200Z 11.4N 125.3W   25 KT  30 MPH - Low (ESE Hilo, Hawaii)
 96H  23/1200Z 12.5N 124.9W   25 KT  30 MPH - Low (ESE Hilo, Hawaii)
120H  24/1200Z 12.6N 124.0W   20 KT  25 MPH - Low (ESE Hilo, Hawaii)

NWS National Hurricane Center Miami FL 200 AM PDT Sat Oct 19, 2019

Dry air and southeasterly shear are taking their toll on Octave. Small bursts of intermittent convection continue to the northwest of Octave’s center, and the lack of persistent deep convection over the center is causing the low to gradually spin down. The latest subjective Dvorak classification from TAFB suggests winds have decreased to 30 kt, with even lower intensity estimates from SAB and UW-CIMSS ADT. Given that the overnight scatterometer missed the system and the fact it does take time to spin down these lows, the initial intensity is lowered generously to 30 kt.

Octave will continue to be in a hostile environment with about 25 kt of southeasterly wind shear and in the presence very dry air for the next few days. This should prevent any deep convection from persisting over the cyclone long enough to maintain the current vortex. Thus, a gradual weakening trend should continue, and Octave may become a remnant low by tonight. Even after the system becomes a remnant low, there could be occasional development of convection. However, at this time it is not believed that this convection will be sufficient enough to cause the cyclone to regenerate. This remnant low is expected to persist through the end of the forecast period.

Octave is drifting northeast and it should remain in a weak flow regime for the entire forecast period. The official NHC forecast shows a meandering motion for the next several days, and the forecast track lies near the various consensus aids.

FORECAST POSITIONS AND MAX WINDS

INIT  19/0900Z 11.5N 126.4W   30 KT  35 MPH - Tropical Storm (ESE Hilo, Hawaii)
 12H  19/1800Z 11.7N 126.0W   25 KT  30 MPH - Tropical Depression (ESE Hilo, Hawaii)
 24H  20/0600Z 11.6N 125.8W   25 KT  30 MPH - Low (ESE Hilo, Hawaii)
 36H  20/1800Z 11.2N 125.7W   25 KT  30 MPH - Low (ESE Hilo, Hawaii)
 48H  21/0600Z 11.0N 125.8W   25 KT  30 MPH - Low (ESE Hilo, Hawaii)
 72H  22/0600Z 11.7N 125.2W   25 KT  30 MPH - Low (ESE Hilo, Hawaii)
 96H  23/0600Z 12.4N 124.8W   25 KT  30 MPH - Low (ESE Hilo, Hawaii)
120H  24/0600Z 13.0N 124.4W   25 KT  30 MPH - Low (ESE Hilo, Hawaii)

NWS National Hurricane Center Miami FL 800 PM PDT Fri Oct 18, 2019

Octave’s convection has waxed and waned since the tropical storm formed yesterday, and it’s once again trending upward. Convection redeveloped in the northwest quadrant of the cyclone during the past few hours, staving off remnant low status for now. The intensity remains 35 kt, based on earlier ASCAT data. The global models indicate that upper-level winds will become unfavorable for the continued maintenance of deep convection on Saturday, so Octave is still not expected to last much longer as a tropical cyclone. The new NHC forecast maintains Octave as a tropical storm for 12 more hours, but this could be generous. Once it becomes a remnant low, occasional disorganized patches of convection will probably be enough to maintain a weak low for at least a few more days, but it is not expected to make any kind of significant comeback.

Octave has continued to move northward, now at 4 kt. The shallow tropical storm is caught between low-level southwesterly flow to its south and easterly trade-wind flow to its north, and the dynamical guidance is in extremely poor agreement on which flow regime will dominate the motion of the cyclone after it becomes post-tropical over the weekend. A few models (including the ECMWF and HMON) forecast that neither regime will dominate and Octave will move very little for the next 5 days. The overall model spread is over 600 miles by day 5, but I have no reason to favor any one track over the others at this point. Therefore, the official track forecast is largely unchanged and lies near the middle of the unusually wide guidance envelope.

FORECAST POSITIONS AND MAX WINDS

INIT  19/0300Z 11.5N 126.6W   35 KT  40 MPH - Tropical Storm (ESE Hilo, Hawaii)
 12H  19/1200Z 11.9N 126.3W   35 KT  40 MPH - Tropical Storm (ESE Hilo, Hawaii)
 24H  20/0000Z 11.9N 126.0W   30 KT  35 MPH - Low (ESE Hilo, Hawaii)
 36H  20/1200Z 11.6N 125.6W   30 KT  35 MPH - Low (ESE Hilo, Hawaii)
 48H  21/0000Z 11.2N 125.6W   25 KT  30 MPH - Low (ESE Hilo, Hawaii)
 72H  22/0000Z 11.4N 126.0W   25 KT  30 MPH - Low (ESE Hilo, Hawaii)
 96H  23/0000Z 12.5N 126.0W   25 KT  30 MPH - Low (ESE Hilo, Hawaii)
120H  24/0000Z 13.0N 125.5W   25 KT  30 MPH - Low (ESE Hilo, Hawaii)

NWS National Hurricane Center Miami FL 200 PM PDT Fri Oct 18, 2019

Tropical Storm Octave’s deep convection dissipated earlier this morning, leaving a well-defined swirl of low clouds in visible satellite imagery. With the degradation of the cyclone’s structure, recent ASCAT data revealed that maximum winds have decreased to 35 kt. A new small burst of convection is going up to the west of the center, but it’s difficult to know if this convection will continue and if it will meet the organizational requirements for a tropical cyclone.

The new NHC forecast leaves open the possibility that Octave could maintain tropical cyclone status for another 24 hours, but it’s probably at least equally likely that the storm could degenerate into a remnant low tonight if convection doesn’t increase substantially. Either way, dry air and increasing shear are expected to cause Octave’s winds to continue decreasing for the next 24 hours, with the remnant low maintaining 25-kt winds through the end of the forecast period.

Octave’s motion has been northward, or 360/4 kt. This motion is likely to be suppressed within the next 12-24 hours as a low-level trough to the north drops southward, and Octave is expected to make a tight clockwise loop during the 5-day forecast period. The updated NHC track forecast is a little east of the previous forecast, moved in the direction of the multi-model consensus aids. However, it should be noted that by day 5, there is a 700 n mi spread between the easternmost HWRF model and the westernmost UKMET model, suggesting that there is quite a bit of uncertainty on exactly where Octave will end up. Fortunately, it is not likely to be a significant cyclone at that time.

FORECAST POSITIONS AND MAX WINDS

INIT  18/2100Z 11.0N 126.6W   35 KT  40 MPH - Tropical Storm (ESE Hilo, Hawaii)
 12H  19/0600Z 11.6N 126.3W   30 KT  35 MPH - Tropical Depression (ESE Hilo, Hawaii)
 24H  19/1800Z 11.9N 125.9W   25 KT  30 MPH - Low (ESE Hilo, Hawaii)
 36H  20/0600Z 11.7N 125.5W   25 KT  30 MPH - Low (ESE Hilo, Hawaii)
 48H  20/1800Z 11.3N 125.4W   25 KT  30 MPH - Low (ESE Hilo, Hawaii)
 72H  21/1800Z 11.1N 125.7W   25 KT  30 MPH - Low (ESE Hilo, Hawaii)
 96H  22/1800Z 11.9N 125.9W   25 KT  30 MPH - Low (ESE Hilo, Hawaii)
120H  23/1800Z 12.9N 125.7W   25 KT  30 MPH - Low (ESE Hilo, Hawaii)

NWS National Hurricane Center Miami FL 200 AM PDT Fri Oct 18, 2019

Convection around the center briefly dissipated earlier tonight, but has since redeveloped with cloud tops colder than -70 C. Octave has a ragged appearance, and it is apparent that some northeasterly shear is affecting the cyclone. A recent ASCAT-A overpass showed several wind vectors of 35-40 kt, and therefore the initial advisory intensity has been raised to 40 kt.

Octave has slowed to a crawl tonight, with an initial motion of 270/01 kt. Weak steering flow will prevail around the cyclone for the next several days, and a meandering motion is expected throughout the forecast period with a total net motion of only about 100 n mi during that time. The official NHC forecast is between the previous forecast and the track consensus guidance, which resulted in only a slight westward shift in the track beyond day 3.

The intermittent bursts of convection are suggesting that the system has been trying to fight off a dry environment. In addition, the shear currently affecting the cyclone is expected to change little in the next 12-18 hours. These moderately negative factors offsetting the warm SSTs should cause Octave to not change much in intensity today. By later tonight, even drier air is expected to begin entraining into Octave’s circulation, and at the same time 20-25 kt southeasterly winds aloft will begin to shear the cyclone. These increasingly hostile conditions should cause weakening to begin, and Octave is forecast to become a remnant low between 48-72 hours. The latest NHC forecast is similar to the previous one, and near the intensity consensus.

FORECAST POSITIONS AND MAX WINDS

INIT  18/0900Z  9.9N 127.1W   40 KT  45 MPH - Tropical Storm (ESE Hilo, Hawaii)
 12H  18/1800Z 10.3N 127.2W   40 KT  45 MPH - Tropical Storm (ESE Hilo, Hawaii)
 24H  19/0600Z 11.0N 127.2W   40 KT  45 MPH - Tropical Storm (ESE Hilo, Hawaii)
 36H  19/1800Z 11.2N 127.0W   35 KT  40 MPH - Tropical Storm (ESE Hilo, Hawaii)
 48H  20/0600Z 11.0N 126.9W   30 KT  35 MPH - Tropical Depression (ESE Hilo, Hawaii)
 72H  21/0600Z 10.6N 127.4W   30 KT  35 MPH - Low (ESE Hilo, Hawaii)
 96H  22/0600Z 10.9N 127.6W   25 KT  30 MPH - Low (ESE Hilo, Hawaii)
120H  23/0600Z 11.2N 127.6W   25 KT  30 MPH - Low (ESE Hilo, Hawaii)

NWS National Hurricane Center Miami FL 800 PM PDT Thu Oct 17, 2019

Satellite imagery indicates that the cyclone located nearly 1500 mi southwest of the southern tip of the Baja California peninsula has become a little better organized. The latest TAFB Dvorak intensity estimate is 2.5/35 kt. Furthermore, late-arriving ASCAT-C data from earlier today showed a few 30-35 kt wind vectors in the northwest quadrant of the cyclone. Based on these data, the intensity estimate is 35 kt, and the system is now Octave, the 15th named storm of the Eastern Pacific hurricane season.

The tropical storm unexpectedly accelerated southwestward for a brief period earlier this afternoon, but it has since resumed a slow westward crawl. Octave is caught in a region of nearly zero net steering flow, and is therefore expected to move very little for the foreseeable future. Due to Octave’s jump to the southwest, the NHC track forecast has been generally adjusted in that direction and is based primarily on a blend of the GFS and ECMWF global models, both of which call for a slow looping track through 120 h.

Octave is located in an environment that could support slight additional strengthening, as shown by the statistical guidance, though the dynamical models suggest it has already peaked. Upper-level convergence and a drier surrounding environment are forecast to become inhibiting factors to the cyclone’s convection in about 48 h, and it could become a remnant low soon after. The NHC intensity forecast has been adjusted only slightly to account for the higher initial intensity and follows the intensity consensus.

FORECAST POSITIONS AND MAX WINDS

INIT  18/0300Z  9.8N 127.2W   35 KT  40 MPH - Tropical Storm (ESE Hilo, Hawaii)
 12H  18/1200Z 10.1N 127.4W   40 KT  45 MPH - Tropical Storm (ESE Hilo, Hawaii)
 24H  19/0000Z 10.7N 127.4W   35 KT  40 MPH - Tropical Storm (ESE Hilo, Hawaii)
 36H  19/1200Z 11.1N 127.1W   35 KT  40 MPH - Tropical Storm (ESE Hilo, Hawaii)
 48H  20/0000Z 11.1N 126.8W   30 KT  35 MPH - Tropical Depression (ESE Hilo, Hawaii)
 72H  21/0000Z 10.6N 126.5W   30 KT  35 MPH - Tropical Depression (ESE Hilo, Hawaii)
 96H  22/0000Z 10.5N 127.0W   30 KT  35 MPH - Tropical Depression (ESE Hilo, Hawaii)
120H  23/0000Z 11.5N 127.0W   25 KT  30 MPH - Tropical Depression (ESE Hilo, Hawaii)

NWS National Hurricane Center Miami FL 200 PM PDT Thu Oct 17, 2019

Conventional satellite imagery and a series of microwave overpasses indicate that the area of low pressure located about 1400 miles southwest of the southern tip of the Baja California peninsula has developed a well-defined center of circulation. The much-improved cloud pattern consists of prominent convective curved bands in the east semicircle and recent bursts of deep convection with cold cloud tops of -70C near the center. Dvorak intensity estimates from both TAFB and SAB support an initial intensity of 30 kt, and advisories are being initiated on a tropical depression at this time.

The intensity forecast is a bit hazy. However, all of the large- scale models and the statistical-dynamical intensity guidance show only slight intensification through the 72 hour period. The inhibiting contribution appears to be a rather dry low- to mid-level surrounding environment. Beyond 72 hours, most of the global and regional models show the cyclone weakening into a remnant low and remaining embedded in the Intertropical Convergence Zone (ITCZ). Consequently, the NHC forecast calls for only modest strengthening into a tropical storm in 12 hours, then weakening back to a depression in 36 hours. Through the remainder of the forecast, the cyclone should degenerate into a remnant low in 3 days or less, as the global guidance shows.

The initial motion appears to be a rather unpredictable slow drift within weak low- to mid-level steering currents while attached to the ITCZ. The global models are unanimous in maintaining an erratic looping track pattern through the entire period, and the official forecast follows suit, based primarily on a blend of the GFS and ECMWF deterministic models.

FORECAST POSITIONS AND MAX WINDS

INIT  17/2100Z 10.1N 126.5W   30 KT  35 MPH - Tropical Depression (ESE Hilo, Hawaii)
 12H  18/0600Z 10.3N 126.8W   35 KT  40 MPH - Tropical Storm (ESE Hilo, Hawaii)
 24H  18/1800Z 10.8N 126.8W   35 KT  40 MPH - Tropical Storm (ESE Hilo, Hawaii)
 36H  19/0600Z 11.4N 126.4W   30 KT  35 MPH - Tropical Depression (ESE Hilo, Hawaii)
 48H  19/1800Z 11.6N 125.9W   30 KT  35 MPH - Tropical Depression (ESE Hilo, Hawaii)
 72H  20/1800Z 11.1N 125.7W   25 KT  30 MPH - Tropical Depression (ESE Hilo, Hawaii)
 96H  21/1800Z 10.9N 125.5W   25 KT  30 MPH - Tropical Depression (ESE Hilo, Hawaii)
120H  22/1800Z 11.7N 124.9W   25 KT  30 MPH - Tropical Depression (ESE Hilo, Hawaii)

Tropical Storm Octave – NWS National Hurricane Center Miami FL 1100 AM PDT Thu Oct 17, 2019

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

Showers and thunderstorms have increased near an area of low pressure located about 1400 miles southwest of the southern tip of the Baja California peninsula. This system has become better organized since last night, and if this trend continues, advisories will likely be issued later today or tonight while it moves little during the next several days.

* Formation chance through 48 hours…high…80 percent. * Formation chance through 5 days…high…80 percent.

NWS National Hurricane Center Miami FL 500 AM PDT Thu Oct 17, 2019

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

Showers and thunderstorms associated with an elongated area of low pressure located about 1400 miles southwest of the southern tip of the Baja California peninsula have become better organized during the past several hours. Environmental conditions are forecast to be conducive for further development and a tropical depression could form the next couple of days while the system moves little.

* Formation chance through 48 hours…medium…40 percent. * Formation chance through 5 days…medium…40 percent.

NWS National Hurricane Center Miami FL 1100 PM PDT Wed Oct 16, 2019

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

An elongated area of low pressure located about 1250 miles southwest of the southern tip of the Baja California peninsula continues to produce disorganized showers and thunderstorms. Environmental conditions are forecast to be conducive for some gradual development of this system during the next few days while the system moves little.

* Formation chance through 48 hours…low…30 percent. * Formation chance through 5 days…medium…40 percent.

NWS National Hurricane Center Miami FL 500 PM PDT Wed Oct 16, 2019

For the eastern North Pacific…east of 140 degrees west longitude: 1. An elongated area of low pressure located about 1250 miles southwest of the southern tip of the Baja California peninsula is producing disorganized showers and thunderstorms. Environmental conditions are forecast to be conducive for some gradual development of this system during the next few days while the system moves little.

* Formation chance through 48 hours…low…20 percent. * Formation chance through 5 days…medium…40 percent.

NWS National Hurricane Center Miami FL 1100 AM PDT Wed Oct 16, 2019

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

A large area of disorganized showers and thunderstorms located about 1200 miles southwest of the southern tip of the Baja California peninsula is associated with a trough of low pressure. Environmental conditions could support some gradual development of this system during the next few days while the system moves little.

* Formation chance through 48 hours…low…10 percent. * Formation chance through 5 days…low…30 percent.

NWS National Hurricane Center Miami FL 500 AM PDT Wed Oct 16, 2019

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

A large area of disorganized showers and thunderstorms located about 1200 miles southwest of the southern tip of the Baja California peninsula is associated with a trough of low pressure. Environmental conditions could support some gradual development of this system during the next few days while the system moves little.

* Formation chance through 48 hours…low…10 percent. * Formation chance through 5 days…low...30 percent.

NWS National Hurricane Center Miami FL 1100 PM PDT Tue Oct 15, 2019

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

A large area of disorganized showers and thunderstorms located about 1200 miles southwest of the southern tip of the Baja California peninsula is associated with a trough of low pressure. Environmental conditions could support some gradual development of this system during the next few days while the system moves little.

* Formation chance through 48 hours…low…10 percent. * Formation chance through 5 days…low…30 percent.

NWS National Hurricane Center Miami FL 500 PM PDT Tue Oct 15, 2019

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

A large area of disorganized showers and thunderstorms located about 1200 miles southwest of the southern tip of the Baja California peninsula is associated with a trough of low pressure. Some gradual development of this system is possible during the next few days while the system moves little.

* Formation chance through 48 hours…low…near 0 percent. * Formation chance through 5 days…low…20 percent.

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

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