Basement-dwelling pseudo-otaku with a thrill for forecasting on the side.
By: KoritheMan , 2:46 AM GMT on October 15, 2013
Tropical Storm Octave continues to move toward the coast of Baja California. As of the latest NHC advisory, the following information was available on Octave:
Wind: 40 mph, with higher gusts
Location: 25.1°N 112.5°W
Movement: NNE at 12 mph
Pressure: 1002 mb
Octave is a highly sheared tropical cyclone. Satellite images show the majority of precipitation is located well northeast of the center over Baja California del Sur and adjoining mainland Mexico. There are some indications that satellite classifications are beginning to drop, which would make sense given the decadent appearance of Octave on satellite imagery.
Figure 1. Latest infrared satellite image of Tropical Storm Octave. Image credit: NOAA's Satellite Services Division (SSD).
Octave continues to experience southwesterly vertical shear in connection with a broad upstream upper-level trough. This general regime is expected to persist during the next couple of days; in addition, CIMSS TPW imagery shows that Octave has continued to ingest an extremely dry airmass from the Pacific marine layer to its west. In combination with increasing land interaction, Octave should lose its status a tropical cyclone within about 24 hours, if not sooner if orographic lifting does not continue to support convection.
Octave is moving north-northeast, and is now centered just off the coast. Now that Octave has been captured by the trough, a continuation of this general motion is expected to persist. After landfall, the cyclone is forecast to shear apart and stall over the rugged terrain of the southern peninsula, while the mid-level center continues northeastward into the westerlies, enhancing rainfall over northwestern Mexico and the southwestern United States.
Intensity forecast and positions
INITIAL 10/14 2100Z 24.6°N 113.0°W 35 KT 40 MPH
12 hour 10/15 0600Z 25.5°N 113.5°W 30 KT 35 MPH
24 hour 10/15 1800Z 26.2°N 113.3°W 30 KT 35 MPH...INLAND
36 hour 10/16 0600Z 26.3°N 113.2°W 25 KT 30 MPH...POST-TROPICAL/REMNANT LOW
48 hour 10/16 1800Z 26.1°N 113.1°W 20 KT 25 MPH...POST-TROPICAL/REMNANT LOW
Figure 2. My forecast track for Octave. Keep in mind that the initial position on my forecast track was based on the 2100Z NHC advisory, so there are naturally going to be some discrepancies, but the general philosophy is still the same. Also, my intensity forecast has been amended to reflect the initial intensity of Octave as of 0300Z.
NHC storm information
WTPZ35 KNHC 150234
TROPICAL STORM OCTAVE ADVISORY NUMBER 9
NWS NATIONAL HURRICANE CENTER MIAMI FL EP152013
800 PM PDT MON OCT 14 2013
...OCTAVE WEAKENING AS IT APPROACHES THE BAJA CALIFORNIA
...HEAVY RAINFALL THE MAIN THREAT...
SUMMARY OF 800 PM PDT...0300 UTC...INFORMATION
ABOUT 40 MI...60 KM WNW OF CABO SAN LAZARO MEXICO
MAXIMUM SUSTAINED WINDS...40 MPH...65 KM/H
PRESENT MOVEMENT...NNE OR 25 DEGREES AT 12 MPH...19 KM/H
MINIMUM CENTRAL PRESSURE...1002 MB...29.59 INCHES
WATCHES AND WARNINGS
CHANGES WITH THIS ADVISORY...
SUMMARY OF WATCHES AND WARNINGS IN EFFECT...
A TROPICAL STORM WARNING IS IN EFFECT FOR...
* SANTA FE TO PUNTA ABREOJOS
A TROPICAL STORM WARNING MEANS THAT TROPICAL STORM CONDITIONS ARE
EXPECTED SOMEWHERE WITHIN THE WARNING AREA...IN THIS CASE WITHIN
THE NEXT 12 HOURS.
FOR STORM INFORMATION SPECIFIC TO YOUR AREA...PLEASE MONITOR
PRODUCTS ISSUED BY YOUR NATIONAL METEOROLOGICAL SERVICE.
DISCUSSION AND 48-HOUR OUTLOOK
AT 800 PM PDT...0300 UTC...THE CENTER OF TROPICAL STORM OCTAVE WAS
LOCATED NEAR LATITUDE 25.1 NORTH...LONGITUDE 112.5 WEST. OCTAVE IS
MOVING TOWARD THE NORTH-NORTHEAST NEAR 12 MPH...19 KM/H...AND THIS
MOTION IS EXPECTED TO CONTINUE THROUGH TONIGHT. ON THE FORECAST
TRACK...THE CENTER OF OCTAVE WILL BE NEAR THE COAST WITHIN THE
WARNING AREA TONIGHT AND EARLY TUESDAY. LITTLE OR NO MOTION IS
EXPECTED LATE TUESDAY OR WEDNESDAY AS THE SYSTEM WEAKENS.
MAXIMUM SUSTAINED WINDS HAVE DECREASED TO NEAR 40 MPH...65 KM/H...
WITH HIGHER GUSTS. ADDITIONAL WEAKENING IS FORECAST...AND OCTAVE IS
EXPECTED TO WEAKEN TO A TROPICAL DEPRESSION ON TUESDAY AND BECOME A
REMNANT LOW BY TUESDAY NIGHT.
TROPICAL STORM FORCE WINDS EXTEND OUTWARD UP TO 70 MILES...110 KM
FROM THE CENTER.
THE ESTIMATED MINIMUM CENTRAL PRESSURE IS 1002 MB...29.59 INCHES.
HAZARDS AFFECTING LAND
RAINFALL...OCTAVE IS EXPECTED TO PRODUCE TOTAL RAIN ACCUMULATIONS OF
3 TO 6 INCHES...WITH ISOLATED MAXIMUM AMOUNTS OF 8 INCHES
POSSIBLE...OVER THE MAINLAND MEXICO STATE OF SONORA. ADDITIONAL
RAIN ACCUMULATIONS OF 1 TO 2 INCHES ARE POSSIBLE WITH OCTAVE OVER
THE CENTRAL AND SOUTHERN BAJA CALIFORNIA PENINSULA...WITH MAXIMUM
STORM TOTAL AMOUNTS OF 8 INCHES.
WIND...TROPICAL STORM CONDITIONS ARE EXPECTED IN PORTIONS OF THE
WARNING AREA THROUGH TONIGHT.
STORM SURGE...A STORM SURGE IS EXPECTED TO PRODUCE COASTAL FLOODING
NEAR AND TO THE EAST OF WHERE THE CENTER MAKES LANDFALL. NEAR THE
COAST...THE SURGE WILL BE ACCOMPANIED BY LARGE AND DANGEROUS WAVES.
SURF...SWELLS GENERATED WILL CONTINUE AFFECT THE WEST COAST OF BAJA
CALIFORNIA SUR INTO TUESDAY. THESE SWELLS ARE LIKELY TO CAUSE LIFE-
THREATENING SURF AND RIP CURRENT CONDITIONS.
NEXT INTERMEDIATE ADVISORY...1100 PM PDT.
NEXT COMPLETE ADVISORY...200 AM PDT.
Tropical Storm Priscilla is moving over the open Pacific ocean without threat to land. As of the latest NHC advisory, the following information was given on Priscilla:
Wind: 40 mph, with higher gusts
Location: 16.2°N 115.8°W
Movement: N at 9 mph
Pressure: 1003 mb
Priscilla remains a sheared tropical cyclone, with satellite and microwave imagery identifying the low-level center along the northeastern edge of the convective canopy. Satellite estimates still support tropical storm intensity, and earlier ASCAT data does not look as impressive in terms of winds as the one from 6z Monday.
Figure 3. Latest infrared satellite image of Tropical Storm Priscilla. Image credit: NOAA's Satellite Services Division (SSD).
As Octave continues to weaken and move overland, the easterly to east-northeasterly shear that has been persistently afflicting Priscilla should diminish, providing the cyclone with a 24-36 hour window for intensification. Although the GFS shows a decent anticyclone forming at 200 mb over the storm during that period, water vapor imagery and CIMSS TPW data show a rather substantial drying in the airmass to the west of Priscilla. In all likelihood, this subsident airmass will prevent Priscilla from becoming a hurricane; dry air entrainment would be further supported by a relaxation of the shear, which would allow for the cyclone to tighten and consolidate its convection and circulation, allowing dry air to more easily permeate the core. Hence, only a modest strengthening is shown, and Priscilla is expected to peak near 45 kt. There is a chance the cyclone could become stronger if the dry air is not as treacherous is forecast, and small cyclones like Priscilla tend to behave rather erratically in terms of intensity. Beyond 48 hours, southwesterly shear is expected to increase again, and that mechanism should combine with cooler waters and dry air to cause Priscilla to become a remnant low in about four days.
Satellite data suggests that Priscilla is still moving toward the north, but with a more westerly component beginning to ensue. This suggests that low- to mid-level ridging is already returning to the north of the tropical cyclone as Octave exits stage right. The global models show the ridge expanding westward over the next few days, allowing Priscilla to move northwest, then take an abrupt dive to the southwest as the ridge gets even stronger. My forecast track will follow that reasoning, but is not as far south or as sharp with the southwestward turn as some of the recent guidance is.
Intensity forecast and positions
INITIAL 10/14 2100Z 15.7°N 115.8°W 35 KT 40 MPH
12 hour 10/15 0600Z 16.3°N 116.2°W 35 KT 40 MPH
24 hour 10/15 1800Z 16.9°N 117.1°W 40 KT 45 MPH
36 hour 10/16 0600Z 17.5°N 118.1°W 45 KT 50 MPH
48 hour 10/16 1800Z 18.1°N 119.2°W 40 KT 45 MPH
72 hour 10/17 1800Z 19.2°N 120.6°W 35 KT 40 MPH
96 hour 10/18 1800Z 18.7°N 121.7°W 30 KT 35 MPH...POST-TROPICAL/REMNANT LOW
120 hour 10/19 1800Z 17.6°N 123.7°W 25 KT 30 MPH...POST-TROPICAL/REMNANT LOW
Figure 4. My forecast track for Priscilla.
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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