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Tropical Storm NORBERT Forecast Discussion Number 2

2014-09-02 22:50:41| National Hurricane Center (East Pacific)

Issued at 200 PM PDT TUE SEP 02 2014 000 WTPZ44 KNHC 022050 TCDEP4 TROPICAL STORM NORBERT DISCUSSION NUMBER 2 NWS NATIONAL HURRICANE CENTER MIAMI FL EP142014 200 PM PDT TUE SEP 02 2014 Satellite images suggest that Norbert has become a little better organized during the day since the center is no longer partially exposed and banding features have become somewhat better defined. Intensity estimates, however, are about the same as 6 hours ago, so the wind speed is kept at 35 kt. Except for moderate northeasterly shear, environmental conditions appear favorable for strengthening for the next couple of days. Intensity guidance is a bit higher than 6 hours ago, with the HWRF now calling for Norbert to become a hurricane. The new NHC forecast will follow the trend of the guidance and shows a higher peak intensity than the last one, between the intensity consensus and the Florida State Superensemble. Norbert has turned northward and has slowed, with an initial motion of about 360/8. The leftward turn should continue overnight, with a west-northwestward track expected in about 24 hours as Norbert comes under the influence of a mid-level high over Mexico. This high weakens somewhat in a couple of days, which could then force Norbert on a more northwestward track. While the bulk of the guidance still shows the center of Norbert passing south of the Baja California peninsula, there has been a northward trend noted in much of the guidance. The NHC forecast is adjusted to the north and now lies north of the model consensus, but is still south of the latest ECMWF forecast. The new NHC track forecast suggests an increasing chance of tropical-storm-force winds in southern Baja California Sur, and a tropical storm watch has been issued for the extreme southern part of the state. FORECAST POSITIONS AND MAX WINDS INIT 02/2100Z 18.5N 106.5W 35 KT 40 MPH 12H 03/0600Z 19.4N 107.2W 40 KT 45 MPH 24H 03/1800Z 20.0N 108.5W 45 KT 50 MPH 36H 04/0600Z 20.5N 109.6W 50 KT 60 MPH 48H 04/1800Z 21.1N 110.5W 55 KT 65 MPH 72H 05/1800Z 22.6N 112.7W 50 KT 60 MPH 96H 06/1800Z 23.6N 114.8W 45 KT 50 MPH 120H 07/1800Z 24.0N 116.8W 35 KT 40 MPH $$ Forecaster Blake

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Tropical Storm DOLLY Forecast Discussion Number 5

2014-09-02 22:45:13| National Hurricane Center (Atlantic)

Issued at 400 PM CDT TUE SEP 02 2014 000 WTNT45 KNHC 022045 TCDAT5 TROPICAL STORM DOLLY DISCUSSION NUMBER 5 NWS NATIONAL HURRICANE CENTER MIAMI FL AL052014 400 PM CDT TUE SEP 02 2014 Tracking the center of Dolly this afternoon has been, to say the least, challenging. Aircraft and scatterometer wind data show that the center of the storm reformed to the south of the previous track and nearer to the middle of the deep convection. Flight-level and SFMR observations support an initial intensity of about 40 kt. Since the center is expected to move inland in less than 12 hours, no significant change in strength is likely before landfall. Once inland, Dolly should weaken fairly rapidly over the mountains of northeastern Mexico and the system could dissipate even sooner than indicated by the NHC forecast. With the center relocation, it is extremely difficult to estimate the initial motion, but my best guess is 270/10 kt. Despite the complex small-scale motions, the large-scale steering pattern remains roughly the same. A mid-tropospheric ridge near the northwestern Gulf of Mexico coast should drive Dolly in a generally westward direction over the next day or two. The official track forecast has been shifted southward due to the center reformation. This lies about in the middle of the track guidance model suite. The primary threat from Dolly will come from heavy rainfall, with precipitation totals possibly approaching 15 inches in a few locations. These rains will likely cause flash flooding and mud slides in regions of mountainous terrain. This threat will continue even after the center moves inland. FORECAST POSITIONS AND MAX WINDS INIT 02/2100Z 22.0N 97.0W 40 KT 45 MPH 12H 03/0600Z 22.0N 98.3W 35 KT 40 MPH...INLAND 24H 03/1800Z 22.0N 99.5W 30 KT 35 MPH...INLAND 36H 04/0600Z 22.0N 100.5W 25 KT 30 MPH...INLAND 48H 04/1800Z...DISSIPATED $$ Forecaster Pasch

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Tropical Storm NORBERT Forecast Discussion Number 1

2014-09-02 16:46:26| National Hurricane Center (East Pacific)

Issued at 800 AM PDT TUE SEP 02 2014 000 WTPZ44 KNHC 021446 TCDEP4 TROPICAL STORM NORBERT DISCUSSION NUMBER 1 NWS NATIONAL HURRICANE CENTER MIAMI FL EP142014 800 AM PDT TUE SEP 02 2014 The area of low pressure located a couple of hundred miles southwest of Manzanillo now has enough organized convection to be considered a tropical cyclone. Although moderate northeasterly shear is present, banding features are in the southern semicircle of the cyclone along with bursts of convection near the center. The initial wind speed is set to 35 kt in accordance with earlier ASCAT data. Norbert has been moving toward the north-northeast or 020/12. Almost all of the guidance show Norbert turning sharply northward and west-northwestward within 24 hours due to the cyclone leaving the ITCZ and becoming steered by a mid-level high over Mexico. The NHC prediction during this time is on the right side of the guidance envelope, mostly because of the initial motion. After that time, there is some uncertainty in the strength of the ridge over northwestern Mexico, which causes some spread in the model tracks of Norbert while it approaches the southern Baja California peninsula. While the NHC forecast is close to the model consensus after 24 hours, it would not be surprising to see later forecasts be adjusted a bit to the north at longer range, given model trends. The environment near Norbert seems mostly favorable for strengthening during the next few days with the cyclone forecast over warm waters with moderate shear. Given this environment, it is a little surprising that none of the more reliable models makes Norbert a hurricane. Since there is some possibility of land interaction and higher shear, the NHC prediction will be a little above the model consensus, but below the highest guidance. FORECAST POSITIONS AND MAX WINDS INIT 02/1500Z 17.5N 106.5W 35 KT 40 MPH 12H 03/0000Z 18.6N 107.0W 40 KT 45 MPH 24H 03/1200Z 19.3N 108.4W 45 KT 50 MPH 36H 04/0000Z 19.6N 109.6W 50 KT 60 MPH 48H 04/1200Z 20.1N 110.5W 50 KT 60 MPH 72H 05/1200Z 21.8N 112.8W 50 KT 60 MPH 96H 06/1200Z 23.0N 115.5W 45 KT 50 MPH 120H 07/1200Z 23.5N 117.5W 40 KT 45 MPH $$ Forecaster Blake

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Tropical Storm DOLLY Forecast Discussion Number 4

2014-09-02 16:38:55| National Hurricane Center (Atlantic)

Issued at 1000 AM CDT TUE SEP 02 2014 000 WTNT45 KNHC 021438 TCDAT5 TROPICAL STORM DOLLY DISCUSSION NUMBER 4 NWS NATIONAL HURRICANE CENTER MIAMI FL AL052014 1000 AM CDT TUE SEP 02 2014 North-northwesterly vertical shear continues to affect the tropical storm, and the low-level center is located near the northwestern edge of a large mass of deep convection. Arc clouds are also noted to be propagating northward from the system which is indicative of the presence of some dry air at mid levels. Based on observations from the aircraft mission from earlier this morning, the current intensity is held at 45 kt, which is a little above the latest Dvorak estimates. Another Air Force Hurricane Hunter mission into Dolly is scheduled in a few hours to check the intensity. Since the system has been able to intensify overnight in spite of the shear, some additional strengthening is certainly possible before landfall. Weakening after the center moves inland could be more rapid than indicated here, due to the mountainous terrain of northeastern Mexico. The motion has been somewhat faster than earlier estimates and is now near 300/14 kt. A mid-level ridge to the north of Dolly should cause a continued west-northwestward motion for the next 24 hours or so and, based on the faster initial motion, the center is likely to cross the coast somewhat earlier than indicated in previous advisories. The current official track forecast is a little ahead of the model guidance but still shows a decrease in forward speed through 36 hours. The primary threat from Dolly will come from heavy rainfall, with precipitation totals possibly approaching 10 inches in a few locations. These rains will likely cause flash flooding and mud slides in regions of mountainous terrain. This threat will continue even after the center moves inland. FORECAST POSITIONS AND MAX WINDS INIT 02/1500Z 23.4N 96.5W 45 KT 50 MPH 12H 03/0000Z 24.0N 97.5W 50 KT 60 MPH 24H 03/1200Z 24.5N 99.0W 40 KT 45 MPH...INLAND 36H 04/0000Z 24.8N 100.5W 25 KT 30 MPH...INLAND 48H 04/1200Z...DISSIPATED $$ Forecaster Pasch

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Tropical Storm DOLLY Forecast Discussion Number 3

2014-09-02 10:45:52| National Hurricane Center (Atlantic)

Issued at 400 AM CDT TUE SEP 02 2014 000 WTNT45 KNHC 020845 TCDAT5 TROPICAL STORM DOLLY DISCUSSION NUMBER 3 NWS NATIONAL HURRICANE CENTER MIAMI FL AL052014 400 AM CDT TUE SEP 02 2014 An Air Force Reserve reconnaissance aircraft investigating the cyclone early this morning found 925 mb flight-level winds of 50-53 kt in the northeast quadrant and adjusted SFMR winds of at least 40 kt. In addition, two ASCAT overpasses at 0313 UTC and 0406 UTC indicated surface winds of 40-41 kt in the eastern quadrant. Based on these wind data, the intensity has been increased to 40 kt, making the cyclone the fourth tropical storm of the 2014 Atlantic hurricane season. These wind data also required the initial position to be relocated about 60 nmi north of the previous track. The initial motion estimate is northwestward or 305/12 kt, which is based on a blend of passive microwave, scatterometer, and conventional satellite fix data. Other than the northward relocation of the center position, the forecast track reasoning remains unchanged from the previous advisories. The tropical storm is expected to gradually turn more toward the west-northwest as Dolly skirts along the southern periphery of a strong mid-level ridge that is located across most of the Gulf of Mexico and the southeastern United States. Landfall along the northeastern coast of Mexico is expected in about 24 hours, followed by dissipation in 48 hours over the rugged terrain of the Sierra Madre Oriental mountains. The NHC forecast track is similar to the consensus model TVCA, and lies roughly in the middle of the guidance envelope. About 20 kt of north-northwesterly vertical shear is affecting Dolly, which has resulted in most of the convection being displaced well to the south and east of the exposed low-level circulation. However, new convection has recently developed near and just to the southeast of the center, and with the shear forecast to decrease to about 15 kt during the next 12 hours, some additional slight strengthening is possible before Dolly makes landfall. The surface wind data from the reconnaissance aircraft and the two scatterometer passes indicate that the tropical-storm-force wind field has expanded significantly in the eastern semicircle. Since the pressure gradient between Dolly and the large high over the Gulf of Mexico is expected to remain quite strong for the next 36 hours or so, the Government of Mexico has extended the tropical storm warning area northward to Barra El Mezquital. However, no additional northward extension of the warning area appears likely at this time. The primary threat from this system is expected to be heavy rainfall, which is likely to cause flash flooding and mud slides over portions of eastern Mexico. FORECAST POSITIONS AND MAX WINDS INIT 02/0900Z 22.6N 94.8W 40 KT 45 MPH 12H 02/1800Z 23.1N 95.9W 45 KT 50 MPH 24H 03/0600Z 23.7N 97.5W 45 KT 50 MPH 36H 03/1800Z 24.1N 98.9W 35 KT 40 MPH...INLAND 48H 04/0600Z...DISSIPATED INLAND $$ Forecaster Stewart

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