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Hurricane Humberto Forecast Discussion Number 20

2019-09-17 16:58:40| National Hurricane Center (Atlantic)

Issued at 1100 AM EDT Tue Sep 17 2019 000 WTNT44 KNHC 171458 TCDAT4 Hurricane Humberto Discussion Number 20 NWS National Hurricane Center Miami FL AL092019 1100 AM EDT Tue Sep 17 2019 An Air Force Reserve reconnaissance aircraft that investigated Humberto earlier this morning found 700-mb flight-level winds of 96 kt and 82-kt surface winds on a dropsonde in the southwestern quadrant, and 81-kt SFMR surface winds in the northwestern quadrant. More importantly, the wind data indicate that Humberto's wind field has expanded significantly and is becoming asymmetric with the largest wind radii now located in the southern semicircle. The aircraft also measured a central pressure of 961 mb, down 18 mb since this time yesterday. The central pressure typically corresponds to an intensity of around 100 kt, but the expansion of the wind field has resulted in little increase in the eyewall wind field for now. Based on these data, the initial intensity has been increased to 85 kt. Humberto has maintained an east-northeastward motion of 075/07 kt. The hurricane is forecast to remain embedded within the mid-latitude westerlies though the forecast period. A deep-layer trough is forecast to dig southward to the west of Humberto in the 24-48 hour period, causing the hurricane to gradually gain latitude and pass just to the northwest of Bermuda in around 36 hours. The models are in excellent agreement on this developing track scenario and are tightly clustered around the previous advisory track. However, the recent expansion of the wind field and the expected additional increase in the wind on the southeast side of Humberto's circulation will result in the island being in near-hurricane-force conditions. By 72 hours and beyond, Humberto will accelerate northeastward over the cold waters of the north Atlantic and interact with a strong frontal system, resulting in the transition into a large extratropical low. The official track forecast is similar to the previous advisory track through 48 hours, and then is a little faster in the 72-120 hour period, close to a blend of the various consensus models. Due to the expansion of Humberto's wind field and large 35-40-n mi wide eye, only modest strengthening is expected during the next 36 hours or so. Although not explicitly shown, Humberto could still become a major hurricane between 24-36 hours when the cyclone will be located over the warmest water of about 29C. Thereafter, gradual wakening is forecast due to cooler waters and strong southwesterly vertical wind shear in excess of 40 kt. However, the typical rate of weakening due to such hostile shear conditions will be tempered owing to the increasing baroclinic forcing in the right-rear entrance region of a polar jet maximum. The new intensity forecast is nearly identical to the previous advisory, and follows a blend of the consensus models HCCA and FSSE. Key Messages: 1. Tropical-storm-force winds are expected to reach Bermuda by Wednesday afternoon, with hurricane conditions possible Wednesday night and Thursday morning. Residents there should follow advice given by local officials. 2. Large swells will increase along the coast of Bermuda by Wednesday. Dangerous breaking waves, especially along south-facing beaches, could cause coastal flooding Wednesday night and Thursday. 3. Swells will continue to affect the northwestern Bahamas and the southeastern coast of the United States from east-central Florida to North Carolina during the next couple of days, creating life- threatening surf and rip current conditions. FORECAST POSITIONS AND MAX WINDS INIT 17/1500Z 30.7N 73.5W 85 KT 100 MPH 12H 18/0000Z 31.1N 72.0W 90 KT 105 MPH 24H 18/1200Z 31.8N 69.4W 95 KT 110 MPH 36H 19/0000Z 33.1N 66.1W 95 KT 110 MPH 48H 19/1200Z 35.3N 62.6W 90 KT 105 MPH 72H 20/1200Z 39.6N 58.4W 70 KT 80 MPH 96H 21/1200Z 43.0N 52.2W 60 KT 70 MPH...POST-TROP/EXTRATROP 120H 22/1200Z 44.5N 40.0W 50 KT 60 MPH...POST-TROP/EXTRATROP $$ Forecaster Stewart

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Tropical Storm Lorena Forecast Discussion Number 1

2019-09-17 16:56:09| National Hurricane Center (East Pacific)

Issued at 1000 AM CDT Tue Sep 17 2019 000 WTPZ45 KNHC 171456 TCDEP5 Tropical Storm Lorena Discussion Number 1 NWS National Hurricane Center Miami FL EP152019 1000 AM CDT Tue Sep 17 2019 First-light 1-minute visible imagery from GOES-W revealed that the disturbance just south of Mexico has developed a well-defined surface center. The system has also developed an extensive convective band stretching from the southwest to the northeast quadrant of the cyclone. A pair of ASCAT passes overnight showed winds were already at tropical-storm strength, so the system has been designated as Tropical Storm Lorena. The initial intensity is set at 35 kt, though the ASCAT data showed winds could actually already be higher than that, so that may be conservative. Lorena is moving quickly toward the northwest, or 305/13 kt. A mid-level ridge centered over the Gulf of Mexico should keep it moving generally northwestward for the next few days, at a slightly slower speed. Most of the dynamical models show this general scenario, however some of the typically reliable track models, including the GFS, seem to have trouble resolving the small cyclone, and show the cyclone moving more west-northwestward. This small difference is important and could be the difference between Lorena directly impacting Mexico or passing just to the southwest. The NHC forecast is on the far right side of the guidance envelope, favoring the ECMWF and UKMET solutions, which seem to have a more realistic current depiction of the tropical cyclone. The NHC forecast is on the far right side of the standard guidance envelope, but is near the middle of the ECMWF ensemble. This brings Lorena very near the Mexico coast in about 2 days and it is possible that the storm could make landfall. At longer ranges the GFS depicts the beginning of a binary interaction between Lorena and the newly-formed depression to the west, however at the moment this does not seem particularly likely, and the NHC forecast favors the ECMWF through day 5 which shows no such interaction. Moderate easterly shear appears to be affecting the tropical storm for now, and this will likely be the primary moderating factor for Lorena's intensity. SSTs are very warm and there is ample moisture, but only slow intensification is likely as long as the shear persists. The NHC forecast therefore shows slow strengthening for the next couple of days. Beyond that time, if the cyclone moves inland, it should quickly weaken or possibly dissipate, but if it stays farther offshore it may have an opportunity to strengthen further. The NHC forecast holds the cyclone nearly steady-state, but it is well below the consensus at day 4 and 5, since most of the intensity models are based on tracks that stay well offshore of Mexico. FORECAST POSITIONS AND MAX WINDS INIT 17/1500Z 13.7N 100.0W 35 KT 40 MPH 12H 18/0000Z 14.8N 101.0W 40 KT 45 MPH 24H 18/1200Z 16.3N 102.4W 45 KT 50 MPH 36H 19/0000Z 17.5N 103.6W 50 KT 60 MPH 48H 19/1200Z 18.5N 104.6W 55 KT 65 MPH 72H 20/1200Z 20.0N 106.3W 55 KT 65 MPH 96H 21/1200Z 21.0N 108.0W 55 KT 65 MPH 120H 22/1200Z 22.0N 110.0W 50 KT 60 MPH $$ Forecaster Zelinsky

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Tropical Depression Fourteen-E Forecast Discussion Number 1

2019-09-17 16:48:08| National Hurricane Center (East Pacific)

Issued at 900 AM MDT Tue Sep 17 2019 000 WTPZ44 KNHC 171448 TCDEP4 Tropical Depression Fourteen-E Discussion Number 1 NWS National Hurricane Center Miami FL EP142019 900 AM MDT Tue Sep 17 2019 Deep convection has intensified over the small area of low pressure that NHC has been monitoring for several days. Both SAB and TAFB estimates indicate that there is now enough organized thunderstorm activity to initiate advisories on a tropical depression, and the initial wind speed of 30 kt matches the overnight scatterometer data and the subjective Dvorak estimates. The initial motion is an uncertain 335/8 kt, with steering provided by a distant low-level ridge to the east. The cyclone is forecast to gradually turn toward the northwest and west-northwest during the next several days as it runs into the southwestern side of a mid- latitude ridge centered over northwestern Mexico. The biggest complication is Tropical Storm Lorena to the northeast, which some of the model guidance, such as the 6Z GFS, shows a binary interaction with at longer term, which could induce a more northward motion. While I can't rule that out, the forecast will stay closer to the models that show less interaction, such as the more westward HWRF and ECMWF solutions, and the NHC forecast is close to a blend of those models. While almost all of the guidance indicates strengthening of this depression into a hurricane in a few days, this forecast is problematic because of the proximity to Lorena. Convective outflow from Lorena could induce more easterly shear than is currently forecast if the tracks get closer together. For now, since the cyclones are forecast to remain a fair distance from one another, this wind speed prediction assumes that the low-shear environment in most of the models materializes, and the forecast follows the corrected-consensus intensity guidance HCCA. FORECAST POSITIONS AND MAX WINDS INIT 17/1500Z 11.9N 108.2W 30 KT 35 MPH 12H 18/0000Z 12.9N 108.9W 35 KT 40 MPH 24H 18/1200Z 14.5N 110.2W 45 KT 50 MPH 36H 19/0000Z 15.7N 111.8W 50 KT 60 MPH 48H 19/1200Z 16.5N 113.0W 55 KT 65 MPH 72H 20/1200Z 17.1N 114.1W 70 KT 80 MPH 96H 21/1200Z 17.3N 115.3W 75 KT 85 MPH 120H 22/1200Z 17.5N 117.0W 60 KT 70 MPH $$ Forecaster Blake

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Tropical Depression Ten Forecast Discussion Number 1

2019-09-17 16:47:10| National Hurricane Center (Atlantic)

Issued at 1100 AM AST Tue Sep 17 2019 000 WTNT45 KNHC 171447 TCDAT5 Tropical Depression Ten Discussion Number 1 NWS National Hurricane Center Miami FL AL102019 1100 AM AST Tue Sep 17 2019 Deep convection associated with the area of low pressure over the central Atlantic has become more persistent and better organized this morning. Data T-numbers from both SAB and TAFB are 2.0 on the Dvorak scale, therefore advisories are being initiated on a tropical depression. The initial intensity is set at 30 kt, in line with the satellite estimates. The depression is forecast to move over gradually increasing sea surface temperatures within a favorable upper-level environment. The only negative factor for intensification appears to be some nearby dry air, but with low shear conditions expected, so steady strengthening is forecast during the next several days. The NHC forecast calls for the depression to become a tropical storm later today, and attain hurricane status within 72 hours. The NHC intensity forecast is in good agreement with the SHIPS and LGEM statistical models. Since the depression is still in the development phase, the initial motion is a somewhat uncertain 295/10 kt. A strong deep-layer ridge to the north of the cyclone should steer the depression generally west-northwestward at a faster forward speed during the next few days. The track guidance is in relatively good agreement through 72 hours, and brings the cyclone near the northern Leeward Islands in about 3 days. By late in the period, the cyclone is expected to reach the western periphery of the ridge, and there is increasing spread among the guidance. The global model ensemble means are along the right side of the envelope while the HWRF and UKMET are along the left side. The NHC track lies close the consensus aids, which is also in good agreement with the latest ECMWF. Interests in the northern Leeward Islands should monitor the progress of this system. FORECAST POSITIONS AND MAX WINDS INIT 17/1500Z 12.9N 44.9W 30 KT 35 MPH 12H 18/0000Z 13.8N 46.1W 35 KT 40 MPH 24H 18/1200Z 14.7N 47.9W 40 KT 45 MPH 36H 19/0000Z 15.5N 50.2W 45 KT 50 MPH 48H 19/1200Z 16.3N 52.9W 55 KT 65 MPH 72H 20/1200Z 18.2N 59.2W 65 KT 75 MPH 96H 21/1200Z 20.2N 64.7W 75 KT 85 MPH 120H 22/1200Z 22.5N 69.0W 80 KT 90 MPH $$ Forecaster Brown

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Hurricane Kiko Forecast Discussion Number 21

2019-09-17 16:37:13| National Hurricane Center (East Pacific)

Issued at 800 AM PDT Tue Sep 17 2019 000 WTPZ43 KNHC 171437 TCDEP3 Hurricane Kiko Discussion Number 21 NWS National Hurricane Center Miami FL EP132019 800 AM PDT Tue Sep 17 2019 Kiko continues to have an irregular shape on satellite imagery, with most of the convection near the center and in the southeastern quadrant of the cyclone. Still, overnight microwave data indicate that the hurricane still has a central core, and the latest satellite estimates support Kiko remaining a 65-kt cyclone on this advisory. Kiko has turned toward the west-southwest this morning due to increased ridging extending from the central Pacific. The synoptic pattern is rather changeable near the tropical cyclone, with a sinuous track anticipated during the next several days due to fluctuations in strength of the subtropical ridge. The forecast has been shifted southward at most times, since the GFS-based guidance has trended toward the ECMWF/UKMET solutions. However, the NHC track is on the northern side of the guidance envelope. The shear that has been affecting Kiko is forecast to relent later today, which should put an end to the weakening trend. By late Wednesday, the cyclone could begin to re-strengthen due to the relaxation of the shear while the storm is over warmer waters. At long range, shear is forecast to increase in about 4 days, causing weakening around that time, although there's little agreement on whether that shear will last. The model guidance is higher at most forecast times than the last cycle, which makes some sense given the southerly adjustment to the track forecast. Thus, the NHC intensity forecast has been adjusted slightly upward, but is below the corrected consensus guidance at most times. FORECAST POSITIONS AND MAX WINDS INIT 17/1500Z 17.0N 125.0W 65 KT 75 MPH 12H 18/0000Z 16.7N 125.8W 60 KT 70 MPH 24H 18/1200Z 16.4N 126.8W 60 KT 70 MPH 36H 19/0000Z 16.3N 127.9W 65 KT 75 MPH 48H 19/1200Z 16.5N 128.9W 65 KT 75 MPH 72H 20/1200Z 17.2N 130.1W 70 KT 80 MPH 96H 21/1200Z 17.3N 131.5W 55 KT 65 MPH 120H 22/1200Z 16.5N 133.0W 55 KT 65 MPH $$ Forecaster Blake

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