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Tropical Storm Peter Forecast Discussion Number 6
2021-09-20 04:51:09| National Hurricane Center (Atlantic)
Issued at 1100 PM AST Sun Sep 19 2021 000 WTNT41 KNHC 200251 TCDAT1 Tropical Storm Peter Discussion Number 6 NWS National Hurricane Center Miami FL AL162021 1100 PM AST Sun Sep 19 2021 Peter is a sheared tropical cyclone. Satellite imagery and microwave data indicate that an earlier convective burst near the center of Peter has collapsed tonight. Although the low-level center is now displaced at least 60 n mi west of the edge of the convective cloud mass, an Air Force Reserve Hurricane Hunter aircraft investigating Peter has found the cyclone is a bit stronger tonight. The aircraft measured flight-level (925 mb) winds of 58 kt and SFMR winds of 45 kt or so. These data support raising the initial intensity to 45 kt for this advisory. Peter's wind field is very asymmetric, with tropical-storm-force winds extending outward up to 120 n mi from the center only in its northeast quadrant. The moderate to strong southwesterly vertical wind shear that is plaguing the system is forecast to persist during the next several days. Thus, despite sufficient oceanic heat content along its forecast track, the official NHC intensity forecast does not show any further intensification. In fact, some gradual weakening is forecast since the system appears likely to struggle sustaining organized convection near its center, as suggested by GFS and ECMWF model simulated satellite imagery. The official NHC intensity forecast has been adjusted upward in the near-term to account for the stronger initial intensity, but otherwise closely follows the HCCA and IVCN aids and shows gradual weakening this week. While the official NHC forecast shows Peter remaining a tropical cyclone through the forecast period, the GFS suggests Peter could struggle to even maintain its closed low-level circulation in the coming days. Therefore, it is plausible that the cyclone could degenerate into an open wave and weaken somewhat quicker than forecast. Peter is moving west-northwestward, or 295/12 kt, along the southwestern periphery of a subtropical ridge over the central Atlantic. This general motion should continue for the next couple of days. Thereafter, the track forecast becomes more challenging. A low- to mid-level ridge is expected to build over the western Atlantic by midweek, which would keep the weakening cyclone on a more northwestward trajectory. But, a mid-level shortwave is forecast to drop southward and erode the southern extent of the ridge, which should eventually draw Peter more northward during the middle and latter parts of the week. There is more spread noted in the track guidance at days 3-5, as the timing of this northward turn is uncertain. The official NHC track forecast has been adjusted slightly to the left of the previous one, and it lies near the center of the guidance envelope and closer to the TVCA and HCCA aids. Based on the latest track, intensity, and wind radii forecasts, no tropical storm watches or warnings are required for the northern Leeward Islands, Virgin Islands, or Puerto Rico at this time. However, locally heavy rain is possible on Monday and Tuesday when Peter is expected to pass to the north of these locations. Key Messages: 1. Rainfall around the southern periphery of Tropical Storm Peter may lead to areas of urban and small stream flooding through Tuesday across Puerto Rico, the Virgin Islands, and the Northern Leeward Islands. FORECAST POSITIONS AND MAX WINDS INIT 20/0300Z 18.6N 58.5W 45 KT 50 MPH 12H 20/1200Z 19.3N 60.6W 40 KT 45 MPH 24H 21/0000Z 20.1N 62.9W 40 KT 45 MPH 36H 21/1200Z 21.0N 65.0W 35 KT 40 MPH 48H 22/0000Z 22.0N 66.7W 35 KT 40 MPH 60H 22/1200Z 23.0N 67.9W 30 KT 35 MPH 72H 23/0000Z 23.9N 68.6W 30 KT 35 MPH 96H 24/0000Z 25.7N 68.5W 25 KT 30 MPH 120H 25/0000Z 28.0N 67.5W 25 KT 30 MPH $$ Forecaster Reinhart
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Tropical Storm Rose Forecast Discussion Number 4
2021-09-20 04:50:08| National Hurricane Center (Atlantic)
Issued at 1100 PM AST Sun Sep 19 2021 000 WTNT42 KNHC 200250 TCDAT2 Tropical Storm Rose Discussion Number 4 NWS National Hurricane Center Miami FL AL172021 1100 PM AST Sun Sep 19 2021 The center of Rose has been very difficult to locate in infrared satellite imagery this evening. However, an earlier ASCAT-A overpass as well as an SSMIS microwave image from around of the time of the previous advisory were both helpful in establishing the initial position, motion, and intensity of the tropical cyclone. Rose's center is located on the eastern edge of the main convective mass due to some southeasterly shear. The ASCAT ambiguity data revealed an area of 30-35 kt winds around the southeastern portion of the circulation, so the wind speed remains 35 kt for this advisory. This is also in agreement with subjective Dvorak T-numbers of T2.5 form both SAB and TAFB. The ASCAT data indicated that Rose is located slightly west of the earlier estimates, and the initial motion estimate is now northwestward or 320/14 kt. The cyclone is forecast to move generally northwestward during the next several days around the southwestern and western portions of a subtropical ridge located over the far eastern Atlantic. After day 4, a strong mid- to upper-level trough over the north-central Atlantic should cause Rose to turn northward. The dynamical models are in reasonably good agreement through about 60-72 hours, but there is growing east-to-west (cross-track) spread after that time. The NHC track forecast is not too different from the previous advisory, and lies close to the various consensus models in deference to the increasing model spread late in the period. Rose has about 24 hours over warm waters and in low vertical wind shear conditions in which to strengthen, and the new NHC intensity forecast for that time is unchanged from before. After 24 hours, increasing westerly shear is likely to result in some gradual weakening. A further increase in shear is anticipated by day 3 as Rose approaches the aforementioned trough. This is likely to result in additional weakening, and Rose is forecast to weaken to a tropical depression by day 4. Some of the global model guidance suggests that weakening could occur faster than indicated below, and it is possible that Rose will degenerate into a remnant low by the end of the forecast period. FORECAST POSITIONS AND MAX WINDS INIT 20/0300Z 15.3N 31.1W 35 KT 40 MPH 12H 20/1200Z 16.9N 32.6W 40 KT 45 MPH 24H 21/0000Z 18.9N 34.2W 45 KT 50 MPH 36H 21/1200Z 20.9N 35.5W 40 KT 45 MPH 48H 22/0000Z 22.6N 36.6W 40 KT 45 MPH 60H 22/1200Z 23.9N 37.5W 40 KT 45 MPH 72H 23/0000Z 25.0N 38.7W 35 KT 40 MPH 96H 24/0000Z 27.1N 40.8W 30 KT 35 MPH 120H 25/0000Z 29.0N 40.5W 30 KT 35 MPH $$ Forecaster Brown
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Summary for Tropical Storm Peter (AT1/AL162021)
2021-09-20 04:49:39| National Hurricane Center (Atlantic)
...AIR FORCE HURRICANE HUNTERS FIND PETER A LITTLE STRONGER... ...PETER EXPECTED TO PASS NORTH OF THE LEEWARD ISLANDS EARLY THIS WEEK... As of 11:00 PM AST Sun Sep 19 the center of Peter was located near 18.6, -58.5 with movement WNW at 14 mph. The minimum central pressure was 1004 mb with maximum sustained winds of about 50 mph.
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Tropical Storm Peter Public Advisory Number 6
2021-09-20 04:49:39| National Hurricane Center (Atlantic)
Issued at 1100 PM AST Sun Sep 19 2021 593 WTNT31 KNHC 200249 TCPAT1 BULLETIN Tropical Storm Peter Advisory Number 6 NWS National Hurricane Center Miami FL AL162021 1100 PM AST Sun Sep 19 2021 ...AIR FORCE HURRICANE HUNTERS FIND PETER A LITTLE STRONGER... ...PETER EXPECTED TO PASS NORTH OF THE LEEWARD ISLANDS EARLY THIS WEEK... SUMMARY OF 1100 PM AST...0300 UTC...INFORMATION ----------------------------------------------- LOCATION...18.6N 58.5W ABOUT 305 MI...485 KM E OF THE NORTHERN LEEWARD ISLANDS MAXIMUM SUSTAINED WINDS...50 MPH...85 KM/H PRESENT MOVEMENT...WNW OR 295 DEGREES AT 14 MPH...22 KM/H MINIMUM CENTRAL PRESSURE...1004 MB...29.65 INCHES WATCHES AND WARNINGS -------------------- There are no coastal watches or warnings in effect. Interests in the northern Leeward Islands, Virgin Islands, and Puerto Rico should monitor the progress of this system. DISCUSSION AND OUTLOOK ---------------------- At 1100 PM AST (0300 UTC), the center of Tropical Storm Peter was located near latitude 18.6 North, longitude 58.5 West. Peter is moving toward the west-northwest near 14 mph (22 km/h). This general motion is expected to continue during the next couple of days, followed by a turn to the northwest with a decrease in forward speed on Wednesday. Data from an Air Force Reserve Hurricane Hunter aircraft indicate that maximum sustained winds have increased to near 50 mph (85 km/h) with higher gusts. Some gradual weakening is forecast during the next several days. Tropical-storm-force winds extend outward up to 140 miles (220 km) primarily to the northeast of the center. The estimated minimum central pressure is 1004 mb (29.65 inches). HAZARDS AFFECTING LAND ---------------------- RAINFALL: Rainfall around the southern periphery of Tropical Storm Peter could produce rainfall totals of 1 to 3 inches, with locally higher amounts possible, across portions of the Northern Leeward Islands, including the Virgin Islands, as well as Puerto Rico through Tuesday. This rainfall may lead to areas of urban and small stream flooding. SURF: Swells generated by Peter are expected to affect the northern Leeward Islands early this week, and then reach the Bahamas by midweek. These swells could cause life-threatening surf and rip current conditions. Please consult products from your local weather office. NEXT ADVISORY ------------- Next complete advisory at 500 AM AST. $$ Forecaster Reinhart
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Tropical Storm Peter Wind Speed Probabilities Number 6
2021-09-20 04:49:39| National Hurricane Center (Atlantic)
Issued at 0300 UTC MON SEP 20 2021 596 FONT11 KNHC 200249 PWSAT1 TROPICAL STORM PETER WIND SPEED PROBABILITIES NUMBER 6 NWS NATIONAL HURRICANE CENTER MIAMI FL AL162021 0300 UTC MON SEP 20 2021 AT 0300Z THE CENTER OF TROPICAL STORM PETER WAS LOCATED NEAR LATITUDE 18.6 NORTH...LONGITUDE 58.5 WEST WITH MAXIMUM SUSTAINED WINDS NEAR 45 KTS...50 MPH...85 KM/H. Z INDICATES COORDINATED UNIVERSAL TIME (GREENWICH) ATLANTIC STANDARD TIME (AST)...SUBTRACT 4 HOURS FROM Z TIME EASTERN DAYLIGHT TIME (EDT)...SUBTRACT 4 HOURS FROM Z TIME CENTRAL DAYLIGHT TIME (CDT)...SUBTRACT 5 HOURS FROM Z TIME WIND SPEED PROBABILITY TABLE FOR SPECIFIC LOCATIONS CHANCES OF SUSTAINED (1-MINUTE AVERAGE) WIND SPEEDS OF AT LEAST ...34 KT (39 MPH... 63 KM/H)... ...50 KT (58 MPH... 93 KM/H)... ...64 KT (74 MPH...119 KM/H)... FOR LOCATIONS AND TIME PERIODS DURING THE NEXT 5 DAYS PROBABILITIES FOR LOCATIONS ARE GIVEN AS OP(CP) WHERE OP IS THE PROBABILITY OF THE EVENT BEGINNING DURING AN INDIVIDUAL TIME PERIOD (ONSET PROBABILITY) (CP) IS THE PROBABILITY OF THE EVENT OCCURRING BETWEEN 00Z MON AND THE FORECAST HOUR (CUMULATIVE PROBABILITY) PROBABILITIES ARE GIVEN IN PERCENT X INDICATES PROBABILITIES LESS THAN 1 PERCENT PROBABILITIES FOR 34 KT AND 50 KT ARE SHOWN AT A GIVEN LOCATION WHEN THE 5-DAY CUMULATIVE PROBABILITY IS AT LEAST 3 PERCENT. PROBABILITIES FOR 34...50...64 KT SHOWN WHEN THE 5-DAY 64-KT CUMULATIVE PROBABILITY IS AT LEAST 1 PERCENT. - - - - WIND SPEED PROBABILITIES FOR SELECTED LOCATIONS - - - - FROM FROM FROM FROM FROM FROM FROM TIME 00Z MON 12Z MON 00Z TUE 12Z TUE 00Z WED 00Z THU 00Z FRI PERIODS TO TO TO TO TO TO TO 12Z MON 00Z TUE 12Z TUE 00Z WED 00Z THU 00Z FRI 00Z SAT FORECAST HOUR (12) (24) (36) (48) (72) (96) (120) - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - LOCATION KT $$ FORECASTER REINHART
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