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Tropical Storm HOWARD Forecast Discussion Number 8

2016-08-02 10:49:35| National Hurricane Center (East Pacific)

Issued at 200 AM PDT TUE AUG 02 2016 000 WTPZ44 KNHC 020849 TCDEP4 TROPICAL STORM HOWARD DISCUSSION NUMBER 8 NWS NATIONAL HURRICANE CENTER MIAMI FL EP092016 200 AM PDT TUE AUG 02 2016 Deep convection has increased and become better organized since the previous advisory with the development of a ragged CDO feature. However, recent ASCAT wind data indicate that the low-level center is displaced near the southern edge of the cloud shield due to some modest southwesterly vertical wind shear. The intensity has been increased to 50 kt based on ASCAT-A and ASCAT-B overpasses around 0600Z. The initial motion estimate is 295/13 kt. Howard is forecast to continue moving in a general west-northwestward motion for the next 48 hours or so and gradually weaken. By 72 hours and beyond, Howard is expected to become a vertically shallow remnant low pressure system that will be steered westward by a expansive subtropical ridge located to the north of the cyclone. The NHC model guidance remains tightly packed and the new forecast track, which lies close to multi-model consensus TVCN, is just an extension of the previous advisory. After the earlier brief convective hiatus while Howard was moving over a cold water pool, the cyclone is now moving over warmer water, which likely has aided in the recent redevelopment of significant convection. Although some additional intensification is possible today, this will be short-lived due to Howard moving over sub-25 deg C sea-surface temperatures and into drier and more stable airmass in 12 hours or so. After that time, the combination of even cooler water and increasing southwesterly wind shear should induce steady weakening, with Howard becoming a post-tropical cyclone by 48 hours. While the remnant low is forecast to move back over SSTs near 26 deg C in 96-120 hours, strong southwesterly shear and a stable air mass should prevent any redevelopment of persistent deep convection. The new intensity forecast is similar to the IVCN consensus model. FORECAST POSITIONS AND MAX WINDS INIT 02/0900Z 18.3N 127.6W 50 KT 60 MPH 12H 02/1800Z 19.3N 129.6W 50 KT 60 MPH 24H 03/0600Z 20.5N 132.3W 45 KT 50 MPH 36H 03/1800Z 21.4N 135.1W 40 KT 45 MPH 48H 04/0600Z 22.1N 137.9W 35 KT 40 MPH...POST-TROPICAL 72H 05/0600Z 22.9N 143.7W 30 KT 35 MPH...POST-TROP/REMNT LOW 96H 06/0600Z 23.2N 149.0W 25 KT 30 MPH...POST-TROP/REMNT LOW 120H 07/0600Z 23.2N 154.3W 25 KT 30 MPH...POST-TROP/REMNT LOW $$ Forecaster Stewart

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Tropical Storm HOWARD Forecast Discussion Number 7

2016-08-02 04:36:06| National Hurricane Center (East Pacific)

Issued at 800 PM PDT MON AUG 01 2016 000 WTPZ44 KNHC 020235 TCDEP4 TROPICAL STORM HOWARD DISCUSSION NUMBER 7 NWS NATIONAL HURRICANE CENTER MIAMI FL EP092016 800 PM PDT MON AUG 01 2016 Visible imagery and a 01/2038 UTC AMSR2 microwave pass show that Howard's center of circulation has become exposed to the west of the cloud canopy. Additionally, the entire western half of the cyclone has become devoid of deep convective banding. It appears that modest westerly shear is impinging on the storm and undercutting the diffluent flow aloft. A blend of the Final-T numbers from both TAFB and SAB yields an initial intensity of 45 kt for this advisory. Some additional strengthening is forecast during the next 12 hours while Howard remains over SSTs greater than 26C. By the 24 hour period, the cyclone is expected to move over cooler sub-24 deg C water. Cooler SSTs and increasing southwesterly shear should induce steady weakening, resulting in Howard degenerating into a post-tropical cyclone in 48 hours, and a remnant low by day 3. After that time, the large-scale models show the remnant low degenerating into a trough of low pressure. The intensity forecast is a little above the previous forecast, but is lower than the IVCN intensity consensus. Satellite position estimates suggest that Howard is moving toward the west-northwest, or 295 degrees, at about 12 kt. Howard is expected to move in a general west-northwestward motion during the next 72 hours along the southern periphery of a subtropical ridge located to the north of the cyclone. Through the remainder of the period, the cyclone is forecast to become a shallow remnant low and turn toward the west following the low-level easterly tradewind flow. The official NHC forecast is quite similar to the previous one, and is hedged toward the TVCN multi-model consensus. FORECAST POSITIONS AND MAX WINDS INIT 02/0300Z 17.7N 126.4W 45 KT 50 MPH 12H 02/1200Z 18.7N 128.2W 50 KT 60 MPH 24H 03/0000Z 20.0N 130.9W 45 KT 50 MPH 36H 03/1200Z 21.1N 133.7W 40 KT 45 MPH 48H 04/0000Z 22.0N 136.4W 35 KT 40 MPH...POST-TROPICAL 72H 05/0000Z 22.9N 142.0W 30 KT 35 MPH...POST-TROP/REMNT LOW 96H 06/0000Z 23.3N 147.1W 25 KT 30 MPH...POST-TROP/REMNT LOW 120H 07/0000Z 23.2N 152.4W 25 KT 30 MPH...POST-TROP/REMNT LOW $$ Forecaster Roberts

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Tropical Storm HOWARD Forecast Discussion Number 6

2016-08-01 23:29:26| National Hurricane Center (East Pacific)

Issued at 200 PM PDT MON AUG 01 2016 000 WTPZ44 KNHC 012129 TCDEP4 TROPICAL STORM HOWARD DISCUSSION NUMBER 6 NWS NATIONAL HURRICANE CENTER MIAMI FL EP092016 200 PM PDT MON AUG 01 2016 Howard's cloud pattern has become less organized since the last advisory. Although the cyclone has plenty of banding features, they are generally confined to eastern half of its circulation. The low-level center has also recently become exposed, possibly due to westerly shear. Satellite classifications are T3.0/45 kt and T3.5/55 kt from SAB and TAFB, respectively. The initial intensity estimate is kept at 45 kt, on the lower end of these estimates because of the cyclone's degraded appearance. The initial motion estimate is 295/11. A subtropical ridge north of Howard is primarily responsible for the cyclone's steering, but a mid- to upper-level low to the west of it has been imparting a greater northerly component of motion. This general motion with some slight increase in forward speed is likely for another couple of days, after which time a turn toward the west is expected. The turn should occur once Howard weakens and becomes a much shallower cyclone embedded in the trade-wind flow. The new NHC track forecast is only adjusted slightly north of the previous one and is quite close to the multi-model consensus. Sea surface temperatures are sufficiently high to allow for some intensification during the next 12 hours or so, but westerly shear over Howard may temper that. Weakening should commence in about 24 hours, and this rate of weakening should soon become faster as the large-scale thermodynamic become increasingly hostile. Remnant low status is forecast in 48 hours, and dissipation is likely just after day 5. The new NHC intensity forecast is somewhat reduced relative to the previous one and is a little lower than the multi- model consensus after 24 hours. FORECAST POSITIONS AND MAX WINDS INIT 01/2100Z 17.2N 125.3W 45 KT 50 MPH 12H 02/0600Z 18.4N 127.1W 50 KT 60 MPH 24H 02/1800Z 19.7N 129.7W 45 KT 50 MPH 36H 03/0600Z 20.8N 132.5W 40 KT 45 MPH 48H 03/1800Z 21.8N 135.4W 30 KT 35 MPH...POST-TROP/REMNT LOW 72H 04/1800Z 22.9N 141.0W 25 KT 30 MPH...POST-TROP/REMNT LOW 96H 05/1800Z 23.3N 146.3W 20 KT 25 MPH...POST-TROP/REMNT LOW 120H 06/1800Z 23.4N 151.6W 20 KT 25 MPH...POST-TROP/REMNT LOW $$ Forecaster Kimberlain

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Tropical Storm HOWARD Forecast Discussion Number 5

2016-08-01 16:43:25| National Hurricane Center (East Pacific)

Issued at 800 AM PDT MON AUG 01 2016 000 WTPZ44 KNHC 011443 TCDEP4 TROPICAL STORM HOWARD DISCUSSION NUMBER 5 NWS NATIONAL HURRICANE CENTER MIAMI FL EP092016 800 AM PDT MON AUG 01 2016 Howard's convective structure has gradually been increasing in organization. The cyclone's cloud pattern is characterized by a long curved band, at the head of which is a clearing around the low-level center. Subjective Dvorak satellite classifications are T2.5/35 kt and T3.5/55 kt from SAB and TAFB, respectively. A blend of these is used to arrive at the initial intensity estimate of 45 kt. The initial motion estimate is 295/09. Howard's primary steering mechanism is the western extension of a subtropical ridge located over the south-central United States, which is imparting a mostly westerly course. However, a mid- to upper-level low west of the cyclone is allowing for a greater northerly component of motion. This general movement with some increase in forward speed is likely during the next 2 days, after which time a turn toward the west is likely. This should occur when Howard weakens and becomes a shallower cyclone in the trade-wind flow. The official NHC track forecast is hardly unchanged from the previous one and is closest to a blend of the GFS and ECMWF model solutions. Ships model output shows some westerly shear over the cyclone, perhaps related to Howard's outrunning the upper-level anticyclone over it. Otherwise, large-scale conditions are expected to be sufficiently conducive for some additional intensification during the next 24 hours or so. By 36-48 hours, Howard should reach much cooler waters and enter an increasingly drier and more stable environment, all of which should lead to weakening. This should result in a fast rate of weakening, and the system is forecast to become post-tropical in 48 hours. The NHC intensity forecast is close to the multi-model consensus in the short term and then follows the LGEM during the weakening phase. FORECAST POSITIONS AND MAX WINDS INIT 01/1500Z 16.7N 123.6W 45 KT 50 MPH 12H 02/0000Z 17.5N 125.4W 50 KT 60 MPH 24H 02/1200Z 18.7N 128.0W 55 KT 65 MPH 36H 03/0000Z 19.9N 130.8W 45 KT 50 MPH 48H 03/1200Z 21.0N 133.6W 40 KT 45 MPH...POST-TROPICAL 72H 04/1200Z 22.3N 139.2W 30 KT 35 MPH...POST-TROP/REMNT LOW 96H 05/1200Z 22.9N 144.8W 25 KT 30 MPH...POST-TROP/REMNT LOW 120H 06/1200Z 22.9N 150.2W 25 KT 30 MPH...POST-TROP/REMNT LOW $$ Forecaster Kimberlain

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Tropical Storm HOWARD Forecast Discussion Number 4

2016-08-01 10:38:31| National Hurricane Center (East Pacific)

Issued at 200 AM PDT MON AUG 01 2016 000 WTPZ44 KNHC 010838 TCDEP4 TROPICAL STORM HOWARD DISCUSSION NUMBER 4 NWS NATIONAL HURRICANE CENTER MIAMI FL EP092016 200 AM PDT MON AUG 01 2016 The cloud pattern of the cyclone has improved since the previous advisory with the low-level center now embedded within a developing central dense overcast feature. Satellite intensity estimates are T3.0/45 kt from TAFB, T2.5/35 kt from SAB, and T2.7/39 kt from UW-CIMSS ADT. Based on these data, the initial intensity has been increased to 35 kt for this advisory, and the cyclone has been upgraded to Tropical Storm Howard, the eighth named storm of the 2016 season and the eighth named storm during the past 30 days as well. The initial motion remains 295/10 kt. There are no significant changes to the previous forecast track or reasoning. Howard is expected to move in a general west-northwestward motion for the next 72 hours along the southern periphery of a deep-layer ridge located to the north of the cyclone. After that time, the cyclone is forecast to become a shallow remnant low over much cooler water and be steered westward by the low-level easterly tradewind flow. The new NHC forecast track is essentially just an extension of the previous advisory track, and lies close to the consensus models and down the middle of the tightly packed guidance envelope. Additional strengthening is forecast today and tonight while Howard remains over SSTs greater than 25.5 deg C. By 36-48 hours, the cyclone will be moving over sub-24 deg C water and into some modest southwesterly vertical wind shear. That combination of unfavorable conditions will induce steady weakening, resulting in Howard degenerating into a post-tropical cyclone by 48 hours and beyond. The official intensity forecast is similar to previous forecast, and closely follows the SHIPS and IVCN consensus intensity models. FORECAST POSITIONS AND MAX WINDS INIT 01/0900Z 16.1N 122.9W 35 KT 40 MPH 12H 01/1800Z 16.8N 124.5W 40 KT 45 MPH 24H 02/0600Z 18.0N 127.0W 45 KT 50 MPH 36H 02/1800Z 19.1N 129.6W 45 KT 50 MPH 48H 03/0600Z 20.2N 132.3W 35 KT 40 MPH...POST-TROPICAL 72H 04/0600Z 21.9N 137.9W 30 KT 35 MPH...POST-TROP/REMNT LOW 96H 05/0600Z 22.6N 143.5W 25 KT 30 MPH...POST-TROP/REMNT LOW 120H 06/0600Z 22.7N 149.6W 25 KT 30 MPH...POST-TROP/REMNT LOW $$ Forecaster Stewart

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